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Full text of "A comparison of fresh and weathered marble from the tweed courthouse"

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A COMPARISON OF FRESH AND WEATHERED MARBLE 
FROM THE TWEED COURTHOUSE 



Robert Lamb Ware 



A THESIS 



in 



Historic Preservation 



Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the 

Requirement for the Degree of 



MASTER OF SCIENCE 



2001 




Supervisor 

A. Elena Charola 

Lecturer in Historic Preservation 



MU>\ri<^v^5 



Reader 

FrarflrCf. Matero 

Associate Professor of Architecture 

Chair, Graduate Group in Historic Preservation 



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Graduate Group Chair 

Frank G; Matero 

Associate Professor of Architecture 



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UNJV6RSfTY 
OF 

PENNSYLVANIA 



Page ii 




CONTENTS 



LlSl OF ILLUSTRATIONS 



Page iii 



ACKNOWLEDGEMENTS 



XV 



PREFACE 



xvii 



Chapter 
I. 



INTRODUCTION 

1. Reasons for Analysis 

2. Methodology 



1 
3 



II. HISTORICAL BACKGROUND 

1. Beginnings (1858-1862) 

2. William Marcy Tweed (1861-1872) 

3. Architecture 

4. Structural Description 

5. Construction Timeline 

6. Tuckahoe and Sheffield Marble 



5 
6 

7 
10 

25 
33 



III. PREVIOUS ANALYSIS AND CLEANING 

L 1981 Exterior Survey by Ammann & Whitney 43 

2. 1989 Cleaning of the Exterior Masonry: Prepreliminary 

Report by Mesick. Cohen, Waite, Architects 48 

3. 1991 Evaluation of Submitted Masonry Samples by 

Masonry Stabilization Services Corporation 54 

4. Observations about Exterior Weathering 57 

IV. ANALYSIS AND OBSERVATIONS 

1. Rationale for Testing Program 68 

2. Testing Program 73 

3. Gathering and Selection of Samples for Analysis 76 

4. Characterization of Samples 79 

a. Fresh Tuckahoe 76 

b. Weathered Tuckahoe 88 

c. Fresh Sheffield 102 

d. Weathered Sheffield 109 

e. Fresh Cherokee 120 

5. Scanning Electron Microscopy 128 

6. X-Ray Diffraction 129 

7. Comparison of Characterizations 135 



V. CONCLUSION 



138 



APPENDICES 



Page iv 

146 



BIBLIOGRAPHY ^^^ 

INDEX ^^^ 



Page V 



ILLUSTRATIONS 



Frontispiece 



Stereoscopic photograph taken circa 1 872. Scrapbook 
Collection, New York Public Library. 



Chapter II 



Figure 
2.1 



2.2 



2.3 



2.4 



2.5 



An October 7. 1871 illustration from Harper's Weekly 

depicting the Tweed Ring's drain on the finances of New York 
City. The photograph in Figure 1 .4 shows how the courthouse 
actually looked at this time. 

A January 6. 1 872 Harper's Weekly illustration depicting Tweed's 
escape from the City Jail. 

An 1 863 daguerrotype of the construction site as seen from 
Broadway. Numerous blocks of marble lie in the yard 
directly behind the fence. A stonecarver's shanty appears to the 
right behind a line of carved elements, and a hoist is seen to the 
left of the image. Stonework has been completed on the first 
floor/ rusticated basement. Courtesy of the Scrapbook 
Collection. New York Public Library. 

Image of the unfinished building taken from an 1873 stereoscopic 
photograph. The columns on the North Portico are not 
completed, and the pediment has yet to be installed. This view 
became emblematic of the plagued construction process. 
Courtesy of the Scrapbook Collection, New York Public 
Library. 

Circa 1900 photograph of the Tweed Courthouse as seen looking 
southwest across Chambers St. Discoloration of the juxtaposed 
Tuckahoe and Sheffield marble is evident even from this 
distance. The granite staircase to Chambers St. was removed 
in the 40' s. Photograph provided courtesy of John G. Waite 
and Associates. 



Page vi 

2.6 Close-up view of the same photograph showing differential 

staining of exterior marble around the second floor windows. 
The darker blocks are probably Sheffield marble. 



Figure 



Chapter III 



3.1 «& 3.2 Discoloration on the north fa9ade. east and west sides of the 

portico. May, 1989. 

3.3 Cleaning test number 10 performed on two blocks of Tuckahoe 

marble at the first floor level, July 1 989. 

3.4 Close-up of cleaning test number 10. Gray discoloration and pock- 

marking are evident. 

3.5 Tuckahoe marble balusters showing extreme degradation due to 

weathering. Characteristic gray discoloration and blackening 
from the accretion of pollutants are evident. Projecting 
elements of both types of marble tend to look alike because of 
pollution staining. Photo taken May, 1989. 

3.6 & 3.7 Chipped pilaster flutes to the left and a chipped rusticated 

basement block to the right. Many of the finer details of the 
Tuckahoe marble have detached due to weathering. The whiter 
substrate has been exposed, revealing the level of discoloration. 
Photos taken May, 1989. 

3.8 Leaf detail with degraded surface showing exposed individual 

grains and iron stains. Weathering has made the surface 
extremely friable. Photo taken August 2000. 

3.9 A smooth but slightly iron-stained sample of Tuckahoe marble in 

the Stone Exposure Test Wall at the NIST. After 50 years of 
exposure, no gray discoloration was visible. The large grains 
are highlighted by the reflection of the sun on the surface. 

3.10 Iron-stained marble, probably Sheffield, interspersed with blocks 

of Tuckahoe. Iron staining may be due to the leaching out of 
ferruginous minerals such as pyrite. Note how the stone has 
been washed white in areas of rain runoff near the Tuckahoe 
marble while the Tuckahoe has remained a solid gray color. 
Photo taken May. 1989. 

3.11 South facade, west end. May, 1989. Extreme staining is visible 

across the entire surface. This type of discoloration is typical 



^ Page vii 

of Lee marble, a stone quarried within 20 miles of Sheffield. 
MA. The south fa9ade exhibits the worst weathering on the 
building. 

3.12 An iron-stained sample of Lee marble in the Stone Exposure Test 

Wall at the NIST. Like the Tuckahoe sample, discoloration 
due to pollution was not noticed. 

3.13 A Sheffield window header that had been covered with bituminous 

bird-proofing. The comer shows the effects of trapped 
moisture. This part of the stone could be removed merely by 
scraping the surface. 

3.14 A combination of blackening and iron-staining on the left is non- 

existent on the right of these two blocks in the center of the 
photograph. The Similar to the iron-stained blocks, rain runoff 
appears to be washing the surface partially. 

3.15 Exposed areas where moisture is likely to collect, such as the 

cornice, show the most intense staining and decay. 

3.16 This photograph illustrates the juxtaposition of different stone 

types that is clear today but which was not obvious at the time 
of construction. Iron-stained blocks in the wall, probably 
Sheffield marble, are visually distinguishable from the gray, 
discolored stone, which is probably Tuckahoe. The window 
jambs both appear to be Tuckahoe, although the one on the left 
is significantly more chipped and discolored. 

3.17 A modillion appears to be splitting at the seams due to continued 

freeze/thaw cycling beneath a hard surface crust of gypsum. 
Note the semicircular patterns of brownish and blackish iron 
deposits due to the diffusion of iron leachates and other 
atmospheric pollutants. 

Table 

3.1 Mineralogical constituents detected using X-Ray Diffraction. 

Ammann & Whitney, 1981. 

3.2 Elements detected using EDXA. Mesick, Cohen, Waite, 1 989. 

3.3 Mineralogical constituents detected using X-Ray Diffraction. 

MSSC, 1981. 

3.4 Basic properties of three marble types. MSSC. 1991 . 



Page viii 



Chapter IV 

Figure 

4,1 A fresh Tuckahoe surface from sample Number 8. 

4 J A typical view of fresh Tuckahoe marble from thin section slide 

T-8. Red stained calcite is interspersed with dolomite. The 
structure appears uniform and crystalline at the top of the 
photomicrograph. In the lower left, the structure appears more 
conglomerated. 5x magnification, cross-polarized light. 

4.3 Calcite and dolomite distinguished by calcite staining. Lamellar 

twinning can be seen in crystals to the right of the 
photomicrograph. The structure is very compact and uniform 
in some areas but less so in others. The grain boundary shows 
no separation between crystals. lOx magnification, cross- 
polarized light. 

4.4 Dolomite, red-stained calcite, and phlogopite at the surface of the 

fresh Tuckahoe sample on slide T-8. Different expansion 
behavior during thermal cycling will probably cause surface 
pitting.This image is an interesting contrast to Figure 4.19, a 
similar but weathered surface. 20x magnification, cross- 
polarized light. 

4.5 Numerous inclusions are seen in the lower half of the picture. The 

green inclusion appears to be tremolite, while the numerous 
oblong inclusions are phlogopite. The variety of minerals 
creates a heterogeneous structure. 5x magnification, cross- 
polarized light. 

4.6 An absence of microcracking is evident in this photomicrograph of 

slide T-8. Vacuum impregnation with blue dye did not reveal 
any fractures. The clean surface is seen in the upper portion of 
the photomicrograph bordered by the blue dye. Close-up of 5x 
magnification, cross-polarized light. 

4.7 A fractured Tuckahoe surface from sample 8 seen in raking light. 

Intragranular cracking is more common than intergranular 
cracking. 7.5x magnification, fiber-optic illumination. 

4.8 Digitized grain boundary image of 1 square cm of Tuckahoe slide 

T-8. 



Page ix 



4.9 Sample 1 . a typical weathered Tuckahoe surface. Individual grains 

have been exposed and rounded. The original white color has 
turned to a yellowish brown. 

4.10 Thin section slide T-4 from the Eidlitz wing. Calcite is 

interspersed with dolomite. The grains are much finer and 
rounder, and fewer inclusions are seen in this sample than in 
the fresh sample. Grains are oriented more or less horizontally. 
Intergranular cracking is indicated by the vacuum impregnated 
blue dye. 1 .25x magnification, plane polarized light. 

4.11 Thin section slide T-12B from the Eidlitz Wing. Again, calcite is 

interspersed with dolomite. Grains show a more or less 
vertical orientation relative to the photomicrograph. 1 .25x 
magnification, cross-polarized light. 

4.12 Thin section slide T- IB. Red-stained calcite is scattered 

throughout, and oblong phlogopite inclusions are visible in the 
lower right. Cracking, seen in blue, seems to emanate from and 
connect the calcite grains. 5x magnification, plane-polarized 
light. 

4.13 Pyrite (left) and phlogopite (right) in a fractured surface of sample 

1 seen under a stereomicroscope. 38x magnification, fiber- 
optic illumination. 

4.14 Slide T- 1 A. a typical weathered specimen with extensive 

microcracking. Crack networks are highlighted by vacuum- 
impregnated blue dye. Oblong phlogopite inclusions are 
visible at the center of the image. The exposed weathered 
surface is at the bottom of the picture. Photomicrograph is 1 cm 
wide, slide is unstained for calcite. 1 .25x magnification, plane- 
polarized light. 

4.15 Intragranular cracking below a weathered surface in thin section 

slide T-IB. taken from an abacus on the North Portico. The 
original grain boundary is shown in yellow, cracks are 
indicated by the presence of blue dye. and intragranular cracks 
are indicated by red arrows. 50x magnification, cross-polarized 
light. 

4.16 Heavy etching, cracking, and iron staining of surface grains, slide 

T-IB. The weathered surface is bordered by the blue dye 
matrix. 5x magnification, plane polarized light. 



Pagex 

4 17 Iron staining and acid etching of surface dolomite crystals on slide 

T-1 B. The surface appears at the top of the slide. Reddish iron 
spots seem to originate in the dolomite crystals themselves. 
Weathering has created an almost sponge-like structure in the 
exposed grains. 20x magnification, plane polarized light. 

4 18 Layers of sulfurous pollution have formed a crust 1 mm thick on 

this surface, from slide T-1 7. A combination of thermal 
expansion and infiltration by soluble salts probably leads to the 
surface decay of Tuckahoe marble. The substrate is seen at the 
bottom and the blue dye matrix is seen at the top. 5x 
magnification, plane-polarized light. 

4 19 Gypsum recrystallization within microcracks. slide T-IB. Due to 

its relative higher solubility, it has penetrated the stone and 
recrystallized. creating additional pressure in the openings. Iron 
spots are also visible. The rhombohedral structure of the 
dolomite grains is seen in the translucent cross-hatching 
patterns. 40x magnification, plane-polarized light. 

4 20 A surface grain of calcite wedged between two surface grains of 

dolomite, slide T- 1 B. The etching of dolomite beneath the 
calcite grain has created a saw-toothed pattern. Recrystallized 
salts are also seen. Thermal dilatation is the most probable 
cause of the microcracking surrounding the calcite grains. The 
space above the calcite grain may have held an ejected 
dolomite grain. 20x magnification, plane-polarized light. 

4J1 Recrystallization of calcite or salts in microcracks. slide T-IB. A 

red stained calcite grain is seen in the center of the photo 
surrounded on either side by white dolomite grains. Gypsum 
appears in a dolomite crack to the bottom right. 40x 
magnification, plane-polarized light. 

4 j2 A fractured surface of sample 1 . Intergranular cracking is more 

common in the weathered sample than in the fresh sample. 
Brown flecks of phlogopite are visible in the cracks. 7.5x 
magnification, fiber-optic illumination. 

4.23 Digitized grain boundary image of 1 square cm of Tuckahoe 

slideT-lB. 

4.24 A fresh Sheffield surface from sample 38. The sample is 

characterized by fine-grained "filler" grains between the larger 
grains. 



Page xi 

4.25 Typical view of fresh Sheffield grains from slide S-38 in cross- 

polarized light. Calcite is seen throughout, and silica is seen 
distributed regularly in blue and orange. 1 .25x magnification, 
unstained for calcite. 

4.26 Intragranular cracking seen on fresh slide S-38. Cracking appears 

to propagate parallel to the bedding plane in this case. 5x 
magnification, plane-polarized light, stained for calcite. 

4.27 A typical fresh fractured Sheffield surface from sample 38. 7.5x 

magnification, fiber-optic illumination. 

4.28 Digitized grain boundary image of 1 square cm of slide S-38. 

4.29 A typical weathered Sheffield surface from sample 37. Exposed 

surface grains have been rounded. The original white color has 
changed to a darker color than the weathered Tuckahoe. 

4.30 Calcite with occasional silica (white) along the grain boundaries on 

slideS-15. Note red staining for calcite. 5x magnificafion, 
plane-polarized light, stained for calcite. 

4.31 Even in the quarry sample S- 1 5, intense microcracking was seen. 

Notice the jumbled of grain sizes and the lack of preferred 
orientation. Cracks are indicated by the vacuum-impregnated 
blue dye. 5x magnificafion, plane-polarized light. 

4.32 * Silica inclusions sometimes appear in bands. Here they are 

gathered in the center and bottom of the slide, S-36. 1 .25x 
magnification, plane-polarized light, stained for calcite. 

4.33 Extreme surface friability on slide S-37. The surface is bordered 

by blue above. Note the predominance of intergranular 
cracking and siliceous inclusions. 5x magnification, plane- 
polarized light, stained for calcite. 

4.34 More extensive intergranular cracking in slide S-37. 1.25x 

magnification, cross-polarized light, unstained for calcite. 

4.35 A typical fractured, weathered Sheffield surface from sample 37. 

7.5x magnification, fiber optic illumination. 

4.36 Digitized grain boundary image of 1 square cm of slide S- 1 5 . 

4.37 A surface grain detaching from the substrate on slide S-36. 

Thermally-induced deformation causes surface grains to fall 



Page xii 

off, opening microcracks that facilitate moisture penetration. 
lOx magnification, plane polarized light, stained for calcite. 

4.38 Etched surface grains oriented at various angles to one another on 

slide S-15. The random orientation of grains may contribute to 
thermally-induced surface damage in Sheffield marble. 5x 
magnification, plane-polarized light, unstained for calcite. 

4.39 Biological growth on the surface of the quarry sample, slide S-15. 

Fungi have digested the first 2 mm of the surface, creating a 
porous substrate. 20x magnification, plane-polarized light, 
stained for calcite. 

4.40 A typical fresh Cherokee surface from sample 36. 

4.41 Crystalline calcite grains (red and orange) and silica inclusions 

(blue, purple, white, yellow). The silica occurs occasionally in 
the Cherokee marble. An unusually dense concentration is 
seen here. The silica forms both along the grain boundaries 
and within the calcite grains. 1 .25x magnification, cross- 
polarized light, stained for calcite. 

4.42 Highly crystalline calcite grains in slide G-26. Note highly 

angular, fused grain boundaries. A siliceous inclusion, seen in 
blue occurs along the grain boundary towards the bottom of the 
photomicrograph. Twinning of calcite is also seen. 50x 
magnification, cross-polarized light, unstained for calcite. 

4.43 Microcracking in fresh Cherokee slide G-29 seen at high 

magnification. Fractures follow the rhombohedral 
mineralogical structure of calcite. 40x magnification, plane- 
polarized light, stained for calcite. 

4.44 A typical fractured surface of Cherokee marble from sample 29. 

4x magnification, fiber-optic illumination. 

4.45 Digitized grain boundary image of 1 square cm of slide G-29. 

4.46 Microscopic decay of fresh Cherokee sample number 26. 

Microcracking of surface grains gives some idea of what might 
happen on a larger scale when the replacement stone weathers. 
40x magnification, plane polarized light, stained for calcite. 

4.47 A block of Georgia Cherokee marble at the NIST Stone Exposure 

Test Wall in Gaithersburg, MD. After 50 years of outdoor 
exposure, the Cherokee block shows surface decay of less than 



Page xiii 

a few microns. No staining from pollution was observed. The 
block is 2 ft. tall. 

4.48 Gypsum encrusted surface of sample 1. lOOx magnification, JEOL 

6400 Analytical SEM. 

4.49 A fresh fractured Tuckahoe surface from sample 1 . Jagged 

intragranular cleavage is seen to the right and top of the image 
and straight intergranular cleavage is seen in the center. 1 OOx 
magnification, JEOL 6400 Analytical SEM. 

4.50 Sample 1 surface with a distinct dolomite grain, center, adjoining a 

micaceous phlogopite inclusion, right. 50x magnification, 
JEOL 6400 Analytical SEM. 

4.51 Distinct calcite crystals on a fractured Sheffield surface from 

sample 37. Fine cleavage planes can be seen between grains. 
lOOx magnification. JEOL 6300FV Field Emission HRSEM. 

4.52 Etching of calcite grains on a weathered Sheffield surface from 

sample 36. Note the outline of an individual calcite crystal in 
the upper left hand of the image. lOOx, JEOL 6300FV Field 
Emission HRSEM. 

4.53 Accretion of pollutants or fine sediment on the weathered surface 

of sample 36. The vague outline of a coated individual crystal 
can be seen in the center of the image. lOOx magnification, 
JEOL 6300FV Field Emission HRSEM. 

Table 

4.1 Summary of Bioquant® data and related measurements for slide T-8. 

4.2 Summary of Bioquant® data and related measurements for slide T-1 B. 

4.3 Summary of Bioquant® data and related measurements for slide S-38. 

4.4 Summary of Bioquant® data and related measurements for slide S-1 5. 

4.5 Summary of Bioquant® data and related measurements for slide G-29. 

4.6 Comparison of Grain Size Summation for the five marble types: G- 

29 Cherokee Fresh; T-8 Tuckahoe Fresh; T-IB Tuckahoe 
Weathered; S-38 Sheffield Fresh; and S-1 5 Sheffield 
Weathered. Grain sizes have been converted to logarithms of 
the actual grain sizes. Both Sheffield curves correspond to each 



Page xiv 

other, as do both Tuckahoe curves. The Cherokee curve is 
noticeably distinct from the rest. 

4.7 Comparison of gradation coefficient, inequality grade, Paris factor, 

grain cohesion, and predominant grain size interval across 
marble type. 



Figure 



Chapter V 



5.1 Dutchman repairs to column flutes on Brooklyn City Hall. The 

one on the right is a closer match with the Tuckahoe. After 
these were installed, extensive retooling was done to reduce the 
starkness of the contrast between the two types of marble. 

5.2 Cherokee replacement abacuses on a Tuckahoe capital. Although 

the difference between the two types of marble is noticeable 
and will become more distinct as the stone weathers, the 
mixture of Cherokee with the Tuckahoe and Sheffield has been 
limited to areas of the building where it will not be noticeable. 



Page XV 



ACKNOWLEDGEMENTS 

Many people have contributed their time, advice, and resources to this paper. 
Foremost among these is my thesis advisor, A. Elena Charola. I am grateful to her for 
agreeing to advise me in the first place. Her prior knowledge of Tuckahoe marble and 
her background in chemisty were invaluable, and our regular conversations helped to 
keep me focused and on track. She was the ideal advisor. I am also thankful to my 
reader, Frank G. Matero, for his editorial input and his advice on the possible directions 
this paper could take. 

The research phase of this project evolved with the help of several key people. I 
would especially like to thank Beth Leahy of Bovis Lend-Lease. Beth provided me with 
unrestricted access to the Tweed Courthouse construction site throughout the year. She 
encouraged my study of the building and shared her time and personal observations with 
me on numerous occasions in person and via e-mail. This paper depended on her help in 
more ways than one. Joan Gemer, also of Bovis, generously arranged for me to work on 
site for a week during the summer, which gave me an opportunity to collect the necessary 
samples. Nancy Rankin at John G. Waite and Associates allowed me to use her firm's 
large photographic archive, which contributed greatly to the graphic content of this paper. 
Jim Zethraus of the Department of General Services allowed me borrow a number of 
reports that were important to understanding the composition and behavior of the Tweed 
marble. Paul Stutzman of the National Institute for Standards and Technology kindly 
provided information about Tuckahoe and Georgia Cherokee marble and gave me a tour 



Page xvi 

of the NIST's Stone Exposure Test Wall. The staff of the Laboratory for Research on the 
Structure of Matter provided assistance with the SEM and XRD portions of the report. 
Rynta Fourie of the Architectural Conservation Laboratory helped me with the 
microscopes and introduced me to Bioquant* software. And Dr. Ben LePage of the 
Earth Sciences Department permitted me to use his department's microscopes, without 
which I would not have been able to take such vivid photomicrographs. 

Above all, I want to thank Anna for her patience with me throughout the graduate 
school process. I could not have done this without her support and encouragement. This 
thesis is dedicated to her. 



Page xvii 



PREFACE 

The current restoration of the Tweed Courthouse, initiated by the Economic 
Development Commission of the City of New York, provides a unique opportunity to 
analyze the comparative weathering of two types of marble. This analysis is especially 
worthwhile because of the nature of the exterior masonry repairs. The city 
govemmenthas been careful to restore and maintain the distinctive architectural features 
of the courthouse as much as its current state will allow. It would not have been 
possible to gather the large number of samples used in this research if the building were 
not undergoing a major restoration. The author hopes that his research will inform an 
appropriate plan for maintenance of the building in the future. 

In the past thirty years, the Tweed Courthouse has begun to receive recognition as 
an outstanding example of 19"^ century architecture. Long neglected because of its 
controversial origins, the courthouse was listed on the National Register of Historic 
Places only seventeen years ago. It stood for decades without any significant exterior 
maintenance and in the 1970's was considered for demolition. Steps to bring the 
building to a level of sustainability were initiated in the late 1980's; the full restoration of 
the building will be completed by the year 2002. The Museum of the City of New York, 
now located on Fifth Avenue and 96"^ St., is scheduled to occupy the courthouse at that 
time. 



CHAPTER I 
Introduction 

Reasons for Analysis 

Much has been written on the subject of marble decay, especially as it concerns 
the European varieties of marble. As far as the decay of North American marbles, and in 
particular those quarried in New York and Massachusetts, considerably less has been 
written. Westchester County, New York marble, commonly known as Tuckahoe marble, 
was used extensively as a building material from the early nineteenth to the early 
twentieth centuries throughout the northeastern United States. Marble from Sheffield, 
Massachusetts, on the other hand, was used only on a limited basis. A lesser-known 
cousin of Lee, Massachusetts marble, Sheffield marble was deemed by the builders of 
Tweed Courthouse to be a comparable material. Whether through aesthetic intent or due 
to external political forces, these two types of stones were used side by side on the same 
building. The result has been an interesting case study in comparative weathering. 

Although Tuckahoe and Sheffield marbles are geologically related, the 
differential weathering observed on the Tweed Courthouse points out the problems of 
using superficial physical and geological characteristics to match stone for exterior uses. 
Mineralogical and microstructural differences in stone samples gathered from distant 
locations within a single geological formation can produce a bewildering diversity in 
observable physical properties. This diversity extends to the level of individual quarries 



Introduction P^g^^ 

and to the level of individual rock strata within those quarries. A marble quarrying 
region such as Westchester County, New York will produce generally similar stone. 
Even so, one quarry may have a reputation for producing durable, architecturally well- 
suited stone while a neighboring quarry may have a reputation for producing stone that is 
fit only for the manufacture of lime. Because they were considered to be similar, 
Tuckahoe and Sheffield marble were used interchangeably during the construction of the 
courthouse. 

Adding complication to any possible analysis, the building was cleaned to a 
general uniformity of color in 1981 and again in 1999 prior to commencement of the 
current restoration. It is therefore difficult to determine the identity of the stone based 
solely on visual observation of the building in its current state. The wide array of 
compositional and behavioral differences in the stone used on the exterior, partially 
masked by these recent efforts to make the building more presentable, leads one to 
question the feasibility of analysis of any kind. Repairs to the exterior of the building are 
being executed with a combination of stone from three sources: salvage stone from the 
building itself; quarried blocks left on the site of the now-defunct Sheffield quarry; and 
entirely new replacement stone from Georgia, known as Georgia Cherokee. It is hoped 
that characterization of the individual rock fabrics of Tuckahoe, Sheffield and Georgia 
marble through thin section analysis will provide a stronger basis for understanding their 
characteristic patterns of weathering. 

This paper is not meant to perform the documentary work of a historic structure 
report. The history of the Tweed Courthouse has been researched and commented on 
thoroughly in a number of ways by professional historians, although much of this 



Introduction ^ ^^g^ ^ 

research remains unavailable to a wide audience. Instead, this paper will focus on the 
microscopic texture of the three types of stone used in the current restoration while 
providing historical information that is contextually relevant to an assessment of the 
observations made. 

For the purposes of this paper, marble from the Eastchester Marble Quarry 
Company used in the construction of the Tweed Courthouse will be referred to as 
Tuckahoe marble. Marble from the Briggs quarry in Sheffield, Massachusetts will be 
referred to as Sheffield marble. The white to gray replacement marble from Georgia will 
be referred to alternately as Georgia Cherokee marble and Cherokee marble. 

Methodology 

This investigation involves two major components: background research and the 
implementation of suitable analysis. The overall goal of the program is to contribute to 
the existing body of knowledge about the texture and fabric of Tuckahoe, Sheffield, and 
Georgia Cherokee marbles and to draw some conclusions about their weathering 
behavior. 

Various archival resources were consulted for the research phase. Primary areas 
of focus were the history of the building and its materials, the history of analysis and 
cleaning related to the building, and the literature pertaining to the study of marble in 
general. The most important source of background information turned out to be the 
project file of the architecture firm overseeing the restoration, John G. Waite & 
Associates of Albany, New York. John G. Waite & Associates has been involved with 
testing, cleaning, and restoration of the Tweed Courthouse for more than ten years. 



Introduction Page 4 

Another important source of information was the project management staff of Bovis 
Lend-Lease, LMB Inc., who have gained an intimate knowledge of the building and the 
unique characteristics of its marble as a result of their involvement with the current 
restoration work. The archive of the Department of General Services of the City of New 
York also provided a great deal of useful information. Other resources include the 
libraries of the University of Pennsylvania, the New York Public Library, Avery Library 
at Columbia University, the National Institute for Standards and Technology, and the 
Federal Highway Administration. Notes, photographs, and interviews made on repeated 
visits to the courthouse also contributed to the research phase. 

The format for the testing and analysis portion of the paper was suggested by the 
existing previous research. Based on this research, it was decided to focus on thin 
section analysis of decayed and fresh samples of the stone. Microscopic thin section 
analysis is one method of petrographic examination that has not been used extensively for 
the study of Tuckahoe or Sheffield marble. By relating texture to weathering 
characteristics, it is hoped that a better understanding of these materials will be gained. 

The first aspect of thin section analysis is visual characterization of 
microstructure, including dominant minerals and inclusions, grain size, grain boundary, 
and microcrack structure. As a complement to thin section analysis, SEM, XRD, and 
EDS were performed on representative samples of marble. 

Most samples for testing and thin section were gathered on site at the Tweed 
Courthouse from discarded original, salvage, and replacement stone. Additional samples 
come from the Briggs quarry in Sheffield, Massachusetts. Resources for analysis and 
testing at the University of Pennsylvania include the Geology Department, the 



Introduction Page 5 

Architectural Conservation Laboratory, and the Laboratory for Research into the 
Structure of Matter. 



CHAPTER II 

Historical Background 



"The house that Tweed buUt was the Boss's legacy to New York, an Acropolis of graft, a shrine to 
boodle. " 

Alexander B. Callow, Jr. 



Long before it was finished in 1881, the New York County Courthouse held a 
place in the imagination of the American public. The building that took twenty years and 
millions of dollars to complete was inextricably linked to the career of William Marcy 
"Boss" Tweed and the political machine that controlled New York City for over a 
decade. Astronomical cost overruns, pocket-lining, and brazen corruption marred the 
reputation of the courthouse long before a single case had been heard in its chambers. 
Helping to spread the building's notoriety was a burgeoning national press led by 
Harper's Weekly. Locally, the New York Times stood alone in chronicling the criminal 
activity of the Tweed Ring. In a series of articles published between 1868 and 1871, the 
Times single-handedly exposed the city government's illicit dealings. As the focal point 
of the Tweed Ring's biggest scandal, the courthouse became a national symbol of 
corruption and moral decay. This sense of decay was mirrored in the behavior of the 
exterior masonry, which began to blacken and weather at an alarming pace even before 
completion. 



Historical Background Page 7 

Beginnings (1858-1862) 

Commercial expansion and population growth fed by European immigration 
during the middle of the 19' century propelled New York City to a level of national 
prominence that it continues to hold today. The growing pains felt by the port city that 
had previously played second fiddle to Boston and Philadelphia manifested themselves in 
a need for better municipal facilities that could accommodate a broader governing 
responsibilities. At the same time, these buildings needed to embody physically the 
city's newfound prominence. As the traditional seat of city government, the area of 
downtown now known as City Hall Park was the site of successive waves of demolition 
and new municipal construction. It was a natural choice for the New York County 
Courthouse, a facility that would symbolize the city's maturity as an economic and 
cultural center. Situated directly behind City Hall, the new courthouse's centrality to 
municipal and county control would be obvious. The triangle of land between Broadway 
and Center and Chambers Streets was the nexus not just of city rule but of a growing 
sphere of governmental influence. 

On April 17, 1858, the Supervisors of the County of New York passed "An Act in 
Relation to the City Hall in the City of New York." ' The act authorized a group of 
commissioners to supervise the erection of a building behind City Hall that would house 
chambers for a number of courts including the Supreme, Superior, Common Pleas, and 
Marine Courts. It would also house the office of the District Attorney and the County 
Sheriff. In 1859, $250,000 out of a projected budget of $1,000,000 was raised towards 



Tweed Courthouse Historic Structure Report (City of New York), 19. 



Historical Background Page 8 

the building's expenses." As is still the practice, construction was financed by the 
issuance of public stock by the city government. Two years later, the Board of 
Supervisors passed the major piece of legislation leading to the creation of the new 
courthouse, an act enabling them to acquire land for the building. In the fall of that year, 
the land was appraised for $450,000. The site encompassed a parcel of land where the 
Second Almshouse (later the New York Institution) once stood and where numerous 
colonial-era paupers' burials took place. 

Construction for the New York County Courthouse began on September 16, 1861. 
During the twenty-year period of the courthouse's construction, the city was required to 
issue stock on numerous occasions to cover ballooning costs. The first of those 
additional issuances took place on April 9, 1862. The city amended the previous act with 
"An Act to Authorize the Board of Supervisors of the County of New York to Raise 
Money by Loan and to Create a Public Fund or Stock to Be Called 'The New York 
County Courthouse Stock,' and to Authorize the Commissioners of the Sinking Fund to 
Receive and Purchase Said Stock. "■* The amended act authorized another $1 million in 
funding. It would be amended again in 1864, 1869, 1870, and 1871 for a total $4.55 
million. These additional issuances of stock still would not take the project to 
completion. 



- Ibid. 

-Ibid., p. 21. 
■* Ibid. 
Laws of the State of New York Passed at the 85''' Session of the Legislature (Albany: Munsell & Rowland, 
1862), pp. 335-337. 



Historical Background 



Page 9 



igCp^rrnri ^i^g^ 




Figure 2.1: An October 7, 1871 illustration from Harper's Weekly depicting the Tweed Ring's drain 
on the finances of New York City. The photograph in Figure 2.4 shows how the courthouse actually 
looked at this time. 



Historical Background Page 10 

William Marcy Tweed (1862-1872) 

The years of William Marcy Tweed's involvement in the construction of the New 
York County Courthouse formed the definitive period in the building's history. If the 
decision to build the new courthouse was motivated by the desire to put a face on 
municipal progress and by the need to deal with growing demands on government, then 
Tweed's skillful manipulation of the mechanics of city finances and implementation of a 
pervasive network of patronage and graft demonstrated just how ill-equipped the city was 
to administer the law. As an architectural manifestation of the city, the courthouse 
showed both how far New York had come and how far it still had to go. 

Tweed was an established figure in national, state, and local politics well before 
he took control of the city's courthouse project. He had already served as Assistant 
Alderman, Congressman, President of the County Board of Supervisors, and Chairman of 
the Democratic Central Committee of New York County. By 1867, six years into the 
project, he was serving as State Senator, New York County Democratic Chairman, 
School Commissioner, Deputy Street Commissioner, and President of the Board of 
Supervisors.^ In the words of The Tweed Courthouse Historic Structure Report, there 
was no man more powerful in New York State politics than "Boss" Tweed. 

In 1861, Tweed was appointed a member of the New York County Board of 

Q 

Supervisors' Special Committee on the New Court House. This position enabled him to 
delve directly into the activities of the new courthouse. On September 23, 1861, three 
days after the Board took possession of the land for the new courthouse, Tweed, acting 



6 



Alexander B. Callow, Jr. The House That Tweed Built (New York, 1871), pp. 17-32. 
Historic Structure Report, p. 8. 
* Ibid., p. 7. 



Historical Background Page 11 

on behalf of the Board of Supervisors, paid John R. Briggs $1,250 for Briggs' Marble 
Quarry, a surface quarrying operation in Sheffield, Massachusetts. Briggs was a New 
York associate of Tweed and an original member of the Tweed "Ring" which voted as a 
block on the Board of Supervisors and bribed Board members to stay away from 
important meetings.'" Subsequently, the city awarded a contract to the quarry for the 
provision of raw quarried marble for use in the construction of the new courthouse." 
This marble was used in addition to another marble from the Eastchester quarries to the 
north of New York City owned and operated by John Masterdon. 

Transactions for the Sheffield marble never appeared in Tweed's name, and he is 
never identified as the owner of the quarry in any of the records, but there is little doubt 
that he ultimately benefited from the city contract. Under an elaborate leasing 
arrangement with Briggs, the existing quarry supervisor, and a man acting for Briggs by 
the name of Henry MacMurray, the City Board would purchase marble from the quarry 
until 1871, at which time ownership of the site and any remaining marble would revert to 
the original purchaser. " In a December 25, 1866 article, however, the New York Times 
reported on a questionable arrangement between the board and the quarry to provide 
stone for the basement.'^ In response, the city appointed a commission to oversee 
construction. The contract was re-advertised for bidding, and two entirely new 



9 



10 



New York Times, December 25, 1866, p. 4. 



Restoration and Rehabilitation of 52 Chambers St (Tweed Courthouse) Prepreliminary Report Masonry 
Cleaning (Albany; Mesick, Cohen, Waite Architects), p. 14, 

In what became his preferred modus operandi, Tweed would buy a controlling interest in a business and 
secure exclusive government contracts with it. A prominent example of this tactic was the New York 
Printing Company. Railroads, ferries, and insurance companies with city or county contracts were required 
to use the services of the Tweed-controlled New York Printing Company or risked losing their contracts 
altogether. See The Dictionary of American Biography (Charles Scribner's Sons), pp. 79-82. 
" Mesick, Cohen, Waite, 12. The architects report refers to the Southern Berkshire Register of Deeds, v. 
125, p. 536. to document the city's original purchase. 

Ibid. The article is referred to in a discussion of the Sheffield quarry in the report byMesick, Cohen, 
Waite. 



Historical Background Page 12 

subcontractors provided the lowest figures . Nevertheless, before the actual work could 
take place, the county supervisors were back in control of the project and one of two 
contracts finally awarded was given to the Sheffield quarry. 

The new contract with Briggs provided that the marble could be billed on a per 
foot basis rather than at a fixed price for the entire scope of work. In terms of cost, this 
was to the Board's advantage since Briggs could remove any percentage markup on the 
stone and presumably the shadow owners would still receive a profit.' Acting on behalf 
of Briggs, Henry MacMurray ran the quarry and signed all deeds and receipts.'^ 
Although it is unclear just how long the quarry provided marble to the city, records show 
that MacMurray sold the quarry in 1866. '^ Strangely, it was granted back to John Briggs 
in 1870. One can assume that Sheffield marble was no longer being shipped to New 
York City after about 1866, an important detail to note in the construction history of the 
building. 

From 1862 to 1870 Boss Tweed consolidated his control over New York City 
government. In 1868, The Board of Supervisors passed the "Adjusted Claims" Act, 
which enabled the city comptroller to adjust any claims against the city and to obtain 
payment by means of the issuance of bonds. The act allowed the city to continue 
selling bonds to cover expenses for the courthouse, effectively extending the source of 
funding indefinitely. Two years later, a new city charter was adopted that abolished the 
County Board of Supervisors and replaced it with the Board of Special Audit which 



'•*Ibid.,p. 13. 

Ibid. Mesick, Cohen, Waite refer to a Report of the Special Committee of the Board of Alderman 
Appointed to Investigate the Tweed Frauds. January 4, 1878, Document 8, (New York: Martin B. Brown), 
p. 47. 
•^Ibid. 
'^ Mesick, Cohen. Waite, p. 13. 

Historic Structure Report, p. 10. 



Historical Background Page 13 

consisted solely of the Mayor, the Comptroller, the Commissioner of Public Works, and 
the President of the Parks Department.'^ Not surprisingly, all of these positions were 
held by Tweed associates. The new charter was dubbed the "Tweed Charter," because of 
the boss's unmistakable influence. 

The area of greatest focus for the Tweed Ring during this period remained the 
new courthouse project. It became a required practice for contractors involved with the 
courthouse to bill an additional 20% on top of their expenses that would go directly to the 
city officials administering the project." This was only a suggested amount, and the 
payments generated by the practice were frequently much higher. Andrew J. Garvey, the 
contractor hired to do the interior plasterwork, also happened to be Grand Marshal of 
Tammany Hall. His excessive bills earned him minor legend status in New York City 
and the nickname the "Prince of Plasterers.""' James H. Ingersoll, another Tweed 
associate and a furniture maker by trade, received more than $5.6 million, about half the 
final estimated cost for the entire building, to fabricate chairs and tables for the 
courtrooms."" Nonexistent contractors received payment as well, and the proceeds went 
directly to the Board of Supervisors. By one estimate, $9 million in graft was expended 
on the construction of the New York County Courthouse."" Many years after the fact, the 
Board of Estimate and Apportionment reported that the entire project probably cost 
between $11 and $12 million.""* 



l' Ib.d. 

"" Historic Structure Report, 1 1 . 



-'Callow, p. 212. 

" Historic Structure Report, 1 1.. 

-■'Callow, p. 197. 

- Historic Structure Report, 21. The HSR refers to the 19 14 Minutes of the Board of Estimate and 

Apportionment of the Cit\' of New York, II, pp 893-97. 



Historical Background Page 14 

This activity did not go without notice. The New York Times and Harper's 
Weekly covered the story locally and nationally. Harper's Weekly utilized the artistic 
abilities of Thomas Nast in covering the story. Political cartoons by Nast and C.G. 
Parker proved to be a true irritant to Tweed, who remarked, ". . .my constituents don't 
know how to read, but they can't help seeing them damned pictures."" An October 7, 
1871 cartoon by C.G. Parker, seen in Figure 1.1, captures the popular sentiment. Despite 
the Tweed Ring's effective efforts to bribe much of the city press, the Times continued to 
cover the story. "^ From early on the Times had criticized the cost overruns and lack of 
substantial progress at the courthouse. An 1867 article in the New York Times 
calculated that for what it cost to construct the New York County Courthouse, 14 
structures identical to Brooklyn's Borough Hall could have been built, furnished and kept 
in repairs for 6 years." 

But in 1 87 1 , what previously had been speculation became impossible to dispute. 
In July of that year, Matthew O'Rourke, a replacement for Ring bookkeeper and ex- 
convict James Watson, went to the Times with a copy of the Comptroller's ledger that he 
had secretly transcribed.'^ Once the contents of the ledger were published in the Times, 
detailing phony payments and illicit transactions, the Ring began to disband. After two 
years of legal wrangling, Tweed was convicted of 204 counts of corruption in the Oyer & 
Terminer court of the still incomplete New York County Courthouse. Despite escaping 
briefly to Cuba and Spain, Tweed spent his final days in the Ludlow Street jail, his name 
and career ruined. Nevertheless, the Tweed name carried on in the New York County 
Courthouse, which was so closely associated with the man and his colorful career. New 



-' Ibid., p. 214. 

-''Callow, p. 214. 

-^ New York Times. May 6, 1867, p. 8. 



' Callow, pp. 259-260. 



Historical Background 



Page 15 



Yorkers could not separate Boss Tweed from the building that had been his domain for 
ten full years, and the New York County Courthouse became known simply as the Tweed 
Courthouse. 

The fallout of the Tweed Ring's financial arrangements eventually extended to 
the provider of the 
Tuckahoe marble used in 



the courthouse. John 
Masterton, second 
generation proprietor of the 
Eastchester Marble Quarry 
Company, was indicted on 
four counts of first-degree 
larceny in 1884."^ 
Masterton had entered a 
banking business with the 
Tweed Ring between 1870 
and 1871. The business. 







Figure 2.1: A January 6, 1872 Harper's Weekly 
illustration depicting Tweed's escape from the City Jail. 



although successful, inexplicably went bankrupt a decade after its chartering. Despite 
this, Masterton continued to receive deposits from investors. As part of the judgment 
against him, he was required to convey the quarry, its buildings and machinery to one of 



his creditors. 



30 



Torres, p. 59. 
Ibid. 



Historical Background Page 16 

Architecture 

Architecturally, the most interesting aspect of the Tweed Courthouse derives from 
the inordinate amount of time it took to complete the building. Spanning the period from 
1858 to 1881, from the first drawings to total completion of the building, the courthouse 
itself can be said to span two distinct stylistic movements in American architecture. 
Originally conceived by the obscure New York architect Thomas Little in the late 1850's, 
the plan was implemented by John Kellum, a popular commercial architect. When 
Kellum passed away in 1873, renowned Victorian architect Leopold Eidlitz refurbished 
and completed the building in a manner more suited to his time. The building displays 
the attitudes of all three of these men. Often described as Anglo-Italianate, the 
courthouse blends a dominant picturesque revivalism with contemporary technological 
breakthroughs in cast-iron and a late 19' century preference for the "organic" 
architecture of the Victorian Romanesque. 

The most significant influence on the design of the New York County Courthouse 
was the United States Capitol building in Washington, D.C. designed by William 
Thornton, Thomas Ustick Walter, and others. To attain the desired level of gravitas, 
government buildings of the mid-nineteenth century often mimicked the Capitol's 
monumentality. The similarities between the two are remarkable. Like the Capitol, the 
courthouse incorporated a central, pedimented portico supported by Corinthian columns. 
A grand staircase leads up to the front entrance of the building, and on either side were 
flanking pavilions. A rusticated basement, pedimented window surrounds, a modillioned 
cornice topped by a balustrade, and a large iron dome are other features of the building 
that it shares with the Capitol. The dome, as it was depicted in Joseph Shannon's 1868 



Historical Background Page 17 

Manual of the Corporation of the City of New York, was never executed. Shannon's 

drawing is the first known pubHshed view of the courthouse, and it is fairly close to the 

completed building. 

Reflecting a shift in taste away from the darker colors of New York's brownstone 

era, the building was designed with a brighter, more timeless material in mind: marble. A 

factor working in marble's favor at this time was the continuing appeal of classical 

revivalism. It is difficult to separate classical revivalism as an architectural movement 

from its use of "noble" building materials like marble. The dominant white aesthetic of 

the Greek Revival, which began to flourish in the 1830's, still had an influence on 

architectural tastes in the 1850's. In 1827, not long after marble deposits were uncovered 

in Westchester County and buildings began to incorporate the local stone, a New York 

weekly noted: 

It is not a little gratifying to an observer to witness the many recent evidences of 
improvement in the style shown in the erection both of public and private edifices. 
Since the discovery of the vast quantities of white marble in Westchester 
County... the effect is everywhere manifest... We anticipate the period when entire 
blocks — nay, whole streets — will show that the provident kindness and liberality 
of nature are moulded to the noblest and most useful purposes. "" 

In the opinion of critics in the 1850's, granite, the dominant building stone of the 30' s 

and 40' s, created a gloomy appearance. White marble's renewed popularity in the 50' s 

soon caused it to eclipse granite in new construction. One contemporary source 

remarked, "We rejoice to see these new materials employed in building; the aspect of the 



Joseph Shannon, Manual of the Corporation of the Cits' of New York, (New York, 1868), p. 639. 
" New-York Mirror and Ladies' Literary' Gazette 5 (December 9, 1827), p. 174. Quoted in Louis Torres, 
Tuckahoe Marble: The Rise and Fall of an Industry. J 822- J 930 (Harbor Hill Books, 1 976), p. 1 3. 
^^ Torres, p. 44. 



Historical Background Page 18 

city is greatly enhanced by their judicious adoption..." ""^ The Westchester marbles also 
had a reputation for durability that compared favorably with other building materials. ^^ 

It is generally agreed that the first person to design the building was Thomas 
Little, an architect whose other surviving buildings include the Italianate New England 
Congregational Church in Brooklyn (1852.) A member of the Board of Supervisors, 
Little came to the project through city politics at a time when the new Capitol was 
gathering praise for its design. He provided an Anglo-Italianate design based on the 
Capitol and on George Dance, Sr.'s Mansion House (1735.) The Italianate palazzo mode 
was widely imitated in London during the decades prior to Little's work on the 
courthouse. Several details confirm Little's presence on the project prior to John Kellum. 
One of these is an article in the New York Times referring to the "original architect" at a 
time when Kellum was in charge of design. In the same article, the large iron dome is 
mentioned as a "recent addition," suggesting that it was among Kellum' s contributions to 
the courthouse. In an 1866 inquiry into misappropriation of funds for construction, 
Thomas Little & Son are named directly by Supervisor Smith Ely, Jr. as the provider of 
the original plans." 

John Kellum assumed responsibility for the execution of Thomas Little's plans in 
1861. It is possible that Kellum' s association with multi-millionaire Alexander T. 
Stewart, whose dry goods department store (1846) still stands across Chambers Street 
from the courthouse, led to his involvement in the city project. Stewart's impressive 



Putnam's Monthly Magazine of American Literature, Science, and Art 1, No. 2, (February 1853), p. 128. 
Quoted in Torres, p. 44. 

■ Contemporary accounts of the durability of Westchester marble are discussed in more detail later in this 
chapter. 

^* New York Times, March 27, 1866, p. 8. The article also mentions a budget not to exceed $800,000, 
identical to the budget for the Brooklyn City Hall (Borough Hall). 

New York City Board of Supervisors, Report of the Special Committee on the Investigation of the 
Contracts for Building the New Courthouse, Doc. No. 9, June 26, 1866, p. 14. Quoted in HSR, p. 43. 



Histor ical Background Page 19 

store, which was built largely of Tuckahoe marble, became known as "The Marble 
Palace. "^^ By 1859, Stewart's business had outgrown the Marble Palace, and he hired 
John Kellum to design a new store in cast-iron at Broadway and 10' Street. This 
commission enabled Kellum to break from Gamaliel King, his partner in King & Kellum, 
and start his own practice in 1 860. With this and other large-scale commercial projects 
under his belt, Kellum must have seemed more suited for the New York County 
Courthouse project than Thomas Little." 

Although in charge of design by 1861, Kellum did not alter much about the 
building's exterior. Joseph Shannon's depiction in the Manual of the Corporation of New 
York City is largely as Thomas Little first drew the building. Little is said to have 
remarked that the only difference between his plan and the completed building was the 
addition of the basement.^ Kellum' s main contributions seem to have been the elevation 
of the building on a rusticated basement similar to the Capitol, the iron dome, which was 
never executed in his lifetime, and the extensive Italianate cast-iron interior. John 
Kellum's use of cast-iron provides an interesting technological juxtaposition to traditional 
Classical Revival design. Cast-iron, while structurally an ideal material for the time, was 
an innovation unknown to the earliest practitioners of the Classical Revival. Its 
extensive incorporation into the plans is one of the most striking aspects of the 
courthouse. The interior is one of the best examples of cast-iron work in the country and 
a major reason for the building's nomination as a National Historic Landmark in 1980. 



^* Torres, p. 34. 

^' Kellum helped design the Cary Building at 105-107 Chambers St., one of the oldest cast-iron buildings in 

the city. Interestingly, Gamaliel King was the architect of Brooklyn City Hall, now known as Borough 

Hall, one of the precedents for the New York County Courthouse. HSR, p. 27. 

^° HSR, p. 43. 



Historical Background Page 20 

Construction dragged on for ten years during Kellum's tenure as chief arciiitect. 
His death in 1871, long before completion, coincided with the dissolution of the Tweed 
Ring. In the culture at large, Kellum's death also coincided with a changing tide in 
American architectural styles. The dominance of picturesque modes ebbed during the 
Victorian era. Less literal, more idiosyncratic quotations of the past started to dominate. 
This was evident in the continuing evolution of the New York County Courthouse. 

Leopold Eidlitz was chosen to take over for John Kellum. Eidlitz, a native of 
Prague, Czechoslovakia, worked in the office of Gothic Revival architect Richard Upjohn 
before starting his own practice. Eidlitz' s mature style was decidedly unique, mixing 
influences from the Gothic Revival and Romanesque Revival modes with a belief in the 
honest "organic" structural expression of these traditions. While his ideas are strikingly 
similar to those of his contemporaries John Ruskin and Viollet-le-Duc, Eidlitz developed 
them independently of their influence.'*' His aesthetic was ". . .the fullest statement of the 
functional-organic view of architecture, based on a medieval-inspired approach to 
structure and composition, produced by any nineteenth-century American." " Eidlitz 
applied this aesthetic in the New York State Capitol Building in Albany (1875) together 
with Henry Hobson Richardson and Frederick Law Olmstead. His main contribution to 
the Capitol was the Assembly Chamber, which is very similar to the wing he would 
design for the Tweed Courthouse. 

It took several years after the Tweed trials for the New York City government to 
regain any enthusiasm for the unfinished county courthouse. By 1876, funding that had 
been appropriated in 1870 was finally allocated to a modified plan for completion. This 



•*' HSR, p. 40. 



42 



William Jordy and Ralph Coe, American Architecture and Other Writings by Montgomei-y Schuyler 



(New York: 1964), p. 17. Quoted in HSR, p. 40. 



Historical Background Page 21 

plan called for an office wing to be built on the south of the building rather than an open 
portico like the one on the north elevation. It also called for completion of the dome. As 
one of New York's most prominent architects, Eidlitz was a natural choice for the 
project. 

The "Eidlitz Wing," as it is now known, was strongly Victorian. Eidlitz' s fantasy 
Romanesque incorporated rounded window arches, ornate floral friezes, and retractable 
awnings on the exterior in an addition that fit four new floors against the three floors of 
the existing building. Eidlitz paid respect to the earlier structure by designing the new 
wing in Tuckahoe marble. Inside, the offices and judges' chambers were sandstone 
groin-vaulted spaces with polychrome brick on the lower floors, and more polychrome 
brick with less sandstone on the higher floors. Encaustic tiled floors were installed 
throughout. Eidlitz also reconceived the courthouse dome. While still made of cast-iron, 
the dome was smaller, took an octagonal, prismatic shape, and rested on squat pillars. 
Beneath the dome hung a pendant stained-glass window. 

Eidlitz's influence was not limited to these areas of the building, however. 
Beyond the work on the new wing, he retrofitted parts of the Kellum Wing to look more 
appropriate to the era. Whole sections of the interior cast iron were torn out and replaced 
with more Victorian materials. The second, third, and attic floors of the rotunda space 
were rebuilt with massive polychrome sandstone pillars and polychrome brick arches. 
The ground floor was redesigned in the same vein as well. 

The criticism aroused by the completed product demonstrates how much 
architectural styles had changed since the days of Thomas Little. The New York Times 



Historical Background Page 22 

scathingly compared the building to a Yorlcville brewery."*^ American Architect and 

Building News wrote: 

Of course no attention was paid to the design of the existing building and within 
and without a rank Romanesque runs cheek by jowl with the old Italian, one bald, 
the other florid; cream-colored brick and buff sandstone come in juxtaposition to 
white marble. "* 

Unfavorable remarks like this combined with a lingering cloud of scandal to keep the 

Tweed Courthouse in disfavor with city politicians. In 188 1 , after twenty long years, the 

building was finally completed. By 1903, it was being targeted for demolition because 

the courts had outgrown the space. Despite its dubious heritage, or perhaps because of it, 

the Tweed Courthouse was able to avoid any major alterations, and it has survived with a 

high degree of integrity. The building's strange agglomeration of styles has aged well, 

and it creates a more harmonious appearance now than it must have 120 years ago. 

Elevations of the courthouse as it appears today are included in Appendix 1 . 

Structural Description 

The Italianate historicism of the Tweed Courthouse belies the 19"^ century 
engineering that supports the design. Masonry and iron construction forms the backbone 
of the building. The high performance of the original structural elements accounts for 
the limited need for any retrofitting during the current restoration. This is partly due to 
the limitations of engineering in the 19'*^ century. By modem standards, the courthouse is 
considerably "over-engineered." Calculations performed in 1981 by Ammann & 
Whitney Consulting Engineers indicate that stresses in the bearing walls are less than 100 



^' New York Times, April 29, 1877, p. 7. Quoted in HSR, p. 67. 

■" American Architect and Building News, III (March 16, 1878), p. 94. Quoted in HSR, p. 67. 



Historical Background Page 23 

pounds per square inch. Even with a mixture of cement and Ume mortars in various 
states of repair in the wall interiors, the walls have considerable reserve capacity. ' The 
massiveness of the primary structure should continue to serve the building well into the 
future. 

The Basement: Beneath the first floor is a basement level which accommodates 
the mechanical plant for the building. The original recirculating hot-air system is located 
here. In the areas of the basement where the ventilation system was installed the floor 
was left uncovered. The large fans for the hot-air system sit on the bare earth of the 
basement, a fact that may have been responsible for early employee complaints about air 
quality in the building.'*^ The basic interior structure of the building is visible at this 
level. A system of massive stone walls, brick walls and arches supports the load of iron 
and masonry on the upper floors. 

The Foundation and First Floor: Exterior access to the building from Chambers 
Street was via the staircase at the North Portico to the second floor, which means that in 
practical usage the first floor was much like a basement. This level is also offset 
architecturally on the exterior by the rustication of the ashlar marble and is aesthetically 
distinct from the higher levels of the building. According to an 1861 New York Times 
article, the exterior foundation contained 6,300 linear feet of Kipp's Bay granite, the 
interior stone walls contained 38,000 cubic feet of mortar and undressed stone, and the 
brick walls contained 650,000 units of brick.^^ 

The Wall and Floor System: The structure of the building is based on traditional 
masonry construction but incorporates untraditional materials for the time, chiefly iron. 



' Ammann & Whitney Consulting Engineers, A Report on the Reconstruction and Improvement to the New 

York Count\' Courthouse (Tweed Courthouse), Technical Report 'B' -Exterior Survey, 1981, p. 1 

•'^ HSR, p. 69. 

•" New York Times, December 27, 1861, p. 4. Quoted in HSR, p. 48. 



Historical Background Page 24 

All of the major walls are predominantly brick up to the level of the roof. The interior 
bearing walls are solid brick with vertical channels for hot air circulation vents and gas 
pipes. According to Ammann & Whitney, the total thickness of the exterior walls ranges 
from about 3' at the roof to 4'-6" at the basement.'*^ Since it would have been impractical 
and far more expensive to use marble as a dimension stone, the exterior walls are brick 
with marble ashlar laid on the granite foundation. The thickness of the ashlar ranges from 
8" to 12."'*^ With the exception of the Corinthian columns on the North Portico, the 
exterior marble does not act as dimension stone. The marble is attached to the brick 
bearing walls with mortar and has no additional pinning or reinforcing. The brick walls 
were constructed integrally with the marble ashlar, and there is no doubt that they are 
mutually reinforcing to some degree. The original steps leading up to the entrance at the 
North Portico were made of Kipp's Bay granite. 

The floor-framing system iron I-beams and girders mimics wood-floor framing in 
a masonry building. Iron for the basement level was provided by the Trenton Iron 
Company of New Jersey. The remainder of the iron, including ornamental and structural 
iron, was provided by John B. and William W. Cornell, who had worked previously with 
John Kellum."^" The floor I-beams weigh 40,000 lbs. apiece and stretch from bearing wall 
to bearing wall. They are in-filled with trabeated brickwork, and a marble floor is laid on 
top of this in the hallways and part of the rotunda. The rest of the rotunda floor is made 
of cast glass-block illuminating tiles set in an iron frame. In the courtrooms, the floors 
are pine board laid on top of concrete supported by trabeated brick and iron. In addition 



'' Ibid. 

''^ Ammann & Whitney, p. 1 . 
'° HSR, p. 50. 



Historical Background Page 25 

to supporting the floor, the iron I-beams provide bracing for the walls. All of the interior 
stairs are iron as well. 

In the Kellum wing of the building, metal lath, an extremely unusual material for 
the time, was attached to the brick walls and covered by a rough "browncoat" of plaster. 
At least one finish coat of plaster was applied to this. The ornate molding, window and 
door frames, and ceiling detailing are all made of cast-iron. 

The Dome and Roof: The dome is an octagonally-shaped frame of cast iron in- 
filled with glass and raised on squat wooden piers, also in-filled with glass. The piers 
were later replaced with cast-iron replicas. Beneath the interior of the dome is a pendant 
stained-glass skylight. Like the majority of the ironwork in the courthouse, the dome was 
fabricated by John B. and William W. Cornell. The original roof was made of corrugated 



iron. 



Construction Timeline 

It is difficult to pinpoint dates for completion of the different portions of the 
Tweed Courthouse, but a great deal of information can be inferred from secondary 
sources and recorded observations. Only one photograph of the phase of construction 
prior to substantial completion, and there are only a handful of depictions and 
photographs of the courthouse from substantial completion to total completion. One 
photo in particular, a view of the building taken circa 1862, provides useful detail about 
the handling of stone and the progress of construction. Many of the dates are drawn from 
the Tweed Courthouse Historic Structure Report, pages 46-75. 



1861 September Ground is broken on the 16' . 



Historical Background 



Page 26 



December 



Year End 



1862 Spring 



1863 September 



November 



Year End 



1865 My 



Mayor Fernando Wood lays the granite comer stone on the 
17th. A block of Tuckahoe marble is placed above this. 
By the end of 1861, all brick, granite, and stone for the 
foundation has been laid. William Tweed purchases the Briggs 
Quarry in Sheffield, Massachusetts. The quarry wins a 
contract to provide marble jointly for the new courthouse, but 
the contract is thrown out and the job is re-bid after Tweed's 
connection to the quarry is exposed. 

Construction is stopped as one of the Commissioners for the 
New Court House retires. The Special Committee on the New 
Court House, under the direction of Supervisor William 
Tweed, assumes oversight of construction. Work does not 
resume until the following year. 

New project specifications, presumably different from previous 
specifications, indicate that "All stone be of white marble,and 
of the very best quality, from either Eastchester, New York 
State, or from Sheffield, Massachussetts Quarries."" 
John Masterdon signs a contract to provide marble from the 
Eastchester Quarry Company to the Courthouse. Henry 
MacMurray, representing the former Briggs Quarry of 
Sheffield, Massachusetts, also signs a contract to provide 
marble for the courthouse. " 

The exterior walls of the first floor and the floor of the second 
floor are complete. Fabrication of architectural marble 
elements from large blocks and finish dressing takes place in 
an area to the west of the building. In a daguerrotype taken 
that year, numerous marble blocks and completed elements are 
seen on the Broadway side of the site stored in the open air 
(Figure 2.3). A small shed apparently serves as a shop for the 
stonecarvers, and a hoist of some kind stands in the center of 
the yard. It is possible that the ashlar marble for the first floor 
is entirely from the Eastchester Quarry since Tuckahoe is the 
first type of stone mentioned as being on site in 1861. 

The shell of the building, comprising the bulk of the exterior 
marble, brick, and other stone work for the Kellum building, is 
complete up to the level of the roof. Iron girders for the floors 
are in place and the fireproof arches of the trabeated brick floor 
are complete. The upper floors can be reached only by a 
ladder. A New York Times reporter visiting the site on July 15 
describes the "polished walls" of marble "high up in the air, 



^' Proceedings of the Board of Superx'isors of New York City, 1861-1868, Doc. 9., pp. 327-338 



52 



Ibid. 



Historical Background 



Page 27 



, "53 



bright and clean as a mirror.""' The North Portico, with its 
Corinthian columns, has not been built. 



1867 March 



Although the building is far from complete. The Court of 
Appeals occupies the southeast comer of the First Floor. The 
main cast-iron stairway is not complete beyond the Second 
Floor, and only a few of the chambers have been stuccoed. The 
large opening in the roof intended for the dome is left 
uncovered, permitting rain and snow to enter the rotunda. 
According to a critical article in the New York Times, the 
courthouse is still without windows and only partially roofed 



over. 



55 



1868 April 



Year End 



1871 April 



One year later, the Times reports that little progress has been 
made and the courthouse is no more than two-thirds complete. 
Large quantities of furniture have been delivered but none of 
the chambers are finished. Only a few workmen, mostly 
painters and glaziers, are still on site. More importantly, the 
Times reports that just 7 years after work began, the exterior 
marble is showing signs of weathering: Already the marble of 
which the Court house is built has become terribly discolored, 
particularly in the east and south sides-quite as much in fact as 
the marble of City Hall, which has been exposed to the 
elements for the last fifty years. This certainly seems to show, 
not withstanding the immense cost of the building and the 
promise that every portion of it should be the very best 
material, that at least in the article of marble an inferior 
quality has been used. 

Marble flooring in the hallways and wood flooring in the 
chambers are installed at the end of the year 



57 



On April 4, a New York Times reporter writes: Up to the 
present time they have completed the front of the building on 
Chambers Street, with the exception of the marble columns, 
and derricks are now being built for these columns, which are 
very handsome and massive, in their places. The Broadway 
front is entirely completed, and the stoops for the back, facing 



City Hall, are being constructed. It appears that the marble 



" New York Times, July 15, 1865, p. 5. 

'■* HSR, p. 52 

'"^ New York Times, March 12, 1867, p. 4. Quoted in HSR, p. 52. 

" All information from New York Times, April 22, 1868, p. 8. Quoted in HSR, p. 52-54. It is especially 

noteworthy that the reporter sees the greatest deterioration on the east and south elevations of the building. 

These are the sides of the building considered to be most in need of repair by the architect during the 

current restoration. Observations on differential weathering are discussed in Chapter 2. 

" HSR, p. 54. 

'* New York Times, April 4, 1 87 1 , p. 2. 



Historical Background Page 28 

for the columns has been carved and is waiting to be installed 
at this point. 

July After the New York Times publishes transactions from the 

ledger of the courthouse project, legal proceedings against 
members of the Tweed Ring begin. The major remaining work 
on the exterior includes completion of the North Portico, 
installation of a Portico on the South, stoops for the south 
pavilion, and the dome. Even so, many courts and several city 
government offices have occupied the building. The rooms are 
largely stuccoed and painted.' 

Fall Several views of the courthouse at this time indicate the degree 

of completion. In an undated stereoscopic photo, derricks 
above the North Portico are visible, as is scaffolding around the 
columns, which have been placed by this time. The pediment 
over the columns is not yet installed. (See Figure 2.4) The 
Ring's financial misdeeds become national news. A 
September drawing and an October political cartoon in 
Harper's Weekly, as well as a drawing from Alexander 
Callow's The House that Tweed Built, published in the same 
year, corroborate the lack of activity. The view of the 
courthouse from Chambers Street, with its inanimate derricks, 
empty scaffolding, and blackening marble, becomes 
emblematic of the troubled project. 

1872 Construction stops completely. 

1873 The Tweed Trial takes place in the Court of Oyer & Terminer. 

The Panic of 1873 increases the unlikelihood that construction 
will be completed in the near future. 

1874 A photograph of City Hall taken from the roof of the Post 

Office Building includes a partial view of the courthouse. The 
derrick above the North Portico is still in place and the 
balustrade on the south fa9ade is incomplete at the pediment. 
The unfinished south pediment awaits the south portico's 
eventual construction. Pilasters on this fagade are complete, 
and the dome still is not installed.^" A suggestion to the Board 
of Aldermen to resume construction is ignored as "unwise 
(and) opposed to the interests of the people. . ." 

1876 July The Commission to Complete the County Courthouse reports 



^ Panorama of New York City, North, East, South and West from the Roof of the Post Office Building, 
Park Row and Broadway, Taken 1874 by W.W. Wilson, Section VI. New York Historical Society. 
^' New York Times, May 15, 1874, p.5. Quoted in HSR, p. 63. 



Historical Background 



Page 29 



that completion of the north portico will be undertaken and 
that, in place of a south portico which would provide no usable 
space, a new wing will be built to accommodate office needs. 
October Contracts are awarded and construction begins. The four large 

entrances to the rotunda space on the first floor are in-filled 
with massive polychrome brick arches. Eidlitz removes large 
sections of the original ironwork to the consternation of city 
officials and architectural critics. 

1877 April The pediment over the Corinthian columns on the north portico 

is put in place. ^" It is unclear from city records who the 
provider of marble for the new south wing is. It is assumed 
that the marble is largely from the Eastchester Quarry 
Company. 

1881 Completion of the Eidlitz improvements to the building takes 

more than twice as long as expected. In the summer of 1881, 
after nearly twenty years of construction, the courthouse is 
complete. Little notice is taken of this fact in the local media. 
A view of the courthouse circa 1900 is provided in Figures 2.4 
and 2.5. 

The timeline brings out several aspects of the construction period as they relate to 

the exterior marble These facts will help to identify the origin of samples gathered from 

the building: 

1) By the time that the 1863 site photo was taken (Figure 2.3), both the Tuckahoe 
marble and the Sheffield marble were specified for construction. It can be assumed that 
both types are present on site at this time and are being used in some combination from 
this point until 1866, when the Briggs Quarry is sold. 

2) It can also be inferred from the sale date of the Briggs Quarry that any marble 
subsequently used did not come from Sheffield, Massachusetts.^"' Sheffield marble is 
most likely to occur on the sections of the building designed by John Kellum and 



^- New York Daily Tribune, April 7, 1877, p.3. Quoted in HSR, p. 65. 

■ While it is possible that stone sat on site for several years and was used later, this is unlikely given the 
typical arrangement between quarry and client. Quarries usually included dressing in their unit price, 
therefore every slab delivered to the site had a predetermined use. Since the quarry provided both services, 
there is little likelihood that Sheffield slabs would have been left on site and dressed by Briggs employees 
after the quarry was sold. 



Historical Background 



Page 30 



executed prior to 1866. This would include the entire building minus the Eidlitz addition, 
the north portico columns and pediment. 

3) This sequence is supported by the photographic record and primary sources, 
which indicate that the columns and pediment for the north portico were not installed 
until 1871-1879. These sections are likely to contain only the Tuckahoe marble. 

4) The time from installation of the exterior marble to manifestation of clear signs 
of weathering was between 3 and 4 years. Substantial completion of the shell occurred in 
1864-1865, and by 1868 obvious blackening and staining were noted. While pollution 
levels in New York City have changed since the 19''' century, it would not be 
unreasonable to see similar discoloration occur within the next ten years. 




Figure 2.2: An 1863 daguerrotype of the construction site as seen from Broadway. Numerous 
blocks of marble lie in the yard directly behind the fence. A stonecarver's shanty appears to the 
right behind a line of carved elements, and a hoist is seen to the left of the image. Stonework has 
been completed on the first floor/ rusticated basement. Courtesy of the Scrapbook Collection, 
New York Public Library. 



Historical Background 



Page 31 




Figure 2.3: Image of the unflnished building taken from an 1873 stereoscopic photograph. The 
columns on the North Portico are not completed, and the pediment has yet to be installed. This 
view became emblematic of the plagued construction process. Courtesy of the Scrapbook 
Collection, New York Public Library. 



Historical Background 



Page 32 




Figure 2.4: A circa 1900 photograph of the Tweed Courthouse as seen looking southwest across 
Chambers St. Discoloration of the juxtaposed Tuckahoe and Sheffield marble is evident even 
from this distance. The granite staircase to Chambers St. seen here was removed during the 
40''s. Photograph provided courtesy of John G. Waite and Associates. 




Figure 2.5: Close-up view of the same photograph showing differential staining of exterior 
marble around the second floor windows. The darker blocks are probably Sheffield marble. 



Historical Background Page 33 

Tuckahoe and Sheffield Marble 

When analyzing the two types of marble used in the construction of the Tweed 
Courthouse, it is helpful to remember their essential relatedness. Tuckahoe and Sheffield 
marbles were installed side by side on the same building largely because of their 
superficial similarity. Both are considered durable, medium to coarse-grained white 
marbles, and both are classified broadly as dolomitic marbles, although this classification 
is less accurate than generally assumed.^"* Both are found in quarries situated along the 
Grenville belt of marble, which was formed during the Cambrian period 500 million 
years ago. Reaching from Quebec to Georgia, the Grenville belt accounts for most of 
the marble quarried in the eastern United States. In the vicinity of New York, the belt is 
exposed at the earth's surface in a strip that runs from In wood at the tip of Manhattan 
northward through portions of western New England and Vermont. Mutual location of 
the Sheffield and Eastchester quarries along this belt accounts for their shared 
mineralogical and behavioral characteristics. 

From the earliest days of its use, marble from Westchester County was valued for 
its color, durability, and workability. Tuckahoe marble, so-called because of the 
proximity of a number of 19' century marble quarries to the village of Tuckahoe, New 
York, has played a large role in the architectural history of the northeastern United States 
and of New York City in particular. Of the Tuckahoe marble quarries, the Eastchester 
Marble Quarry Company is the most well-known. Tuckahoe marble gained a favorable 



A summary of previous mineralogical tests performed on samples from the courthouse is presented in 
Chapter 3. 

" Urquhart, Gordon Ross. The Architectural Histon- of the Westchester Marble Industry. Unpublished 
Master's Thesis, School of Architecture, Columbia University, 1986, p. 5. 
^ Ibid. 



Historical Backg round Page 34 

reputation as a building material during the 19"^ century and was specified for use in 

buildings as far away as Charleston, South Carolina and New Orleans, Louisiana. 

In 1824, soon after the discovery of marble in the area of current day Westchester 

County, S.L Mitchell remarked on some of the characteristics of the stone. He described 

it as, 

. . .granular, the result of incipient or compressed crystallization. It is wholly free 
from shells, crusts and all sorts of organic remains. A fresh fracture exhibits 
many shing surfaces, glistening in the sunshine. It is remarkably free from 
impregnation by iron; and even a small speck or lump of permanent and 
indecomposable pyrites, is a rarity. The color is white; and the stripes of other 
hues that sometimes occur, are inconsiderable, and easily avoided in quarrying. 
The material is exceedingly compact; and as the proof of its durability, the edges 
of the strata which have been exposed to the atmosphere for ages, seem to be 
unaltered by the elements, and to be as coherent and solid as ever. ^^ 

Agreement on a proper geological description of Tuckahoe marble has never been 
clear. Marbles are broadly made up of metamorphic carbonate rocks formed by the 
recrystallization of calcite (CaC03) or dolomite (CaMg(C03)2) through some 
combination of heat and pressure. They must be capable of taking a polish, although 
limestones and dolomites capable of taking a polish are often classified as marbles by the 
building trades. The American Society for Testing and Materials defines calcitic marble 
as containing 5 percent or less magnesium carbonate; marble with between 5 and 40 
percent magnesium carbonate is considered magnesium or dolomitic marble, and those 
with more than 40 percent are dolomite marbles. ^^ 



" Torres, pp 30, 33, and 52. The Custom House in Charleston (1870) was constructed with marble from 
Hastings and Eastchester, NY. The front facade and portico of New Orleans City Hall (1845), now known 
as Gallier Hall, is made of Tuckahoe marble from the Eastchester Marble Quarry Company. Tuckahoe 
marble was also used for the Andrew Jackson Memorial (1855) and the interior of the New Orleans Custom 
House (1854). 

S.L. Mitchill, The Quarries Situated Between East-Chester and the River Bronx. New York, August 19. 
1824. Eastchester Historical Society, Eastchester, New York. Quoted in Torres, p. 13. 
^^ Ammann & Whitney, p. 3. 



Historical Background Page 35 

Variously described as crystalline limestone, dolomitic limestone, limestone, 

marble, and dolomitic marble, Tuckahoe marble is most accurately described as a 

dolomitic marble. The surface graininess and friability commonly observed in some 

weathered specimens of Westchester marble have led to a desire to characterize them 

separately from more common marbles. Nevertheless, the stone fits accepted criteria for 

classification as a dolomitic marble, and some of the earliest observers of Tuckahoe 

marble were correct in their descriptions of it as such. Geologist John Strong Newberry 

noted of the location of the Westchester marble quarries along the Achaean belt of 

dolomite. In 1841, state geologist Lewis C. Beck characterized the stone's mineralogical 

classification and considered it without doubt to be marble: 

...all the varieties belong to what are called the primitive class, and most, if not 
all of them, contain a portion of magnesia, and are thus properly named 
dolomites. . . . Blocks can be obtained of almost any shape and these are 
susceptible of a sufficient polish for building purposes. 

The Tenth Census also describes the stone as dolomitic containing small amounts of iron 
and mica.^' Because the Eastchester Marble Quarry Company comprised at least four 
separate quarries in the vicinity of the villages of Eastchester and Tuckahoe, the 
likelihood of variation in mineralogy and texture is high. This fact, exacerbated by the 
length of construction, may account for the diversity of stone types used in the 
construction of the Tweed Courthouse. ' 



™ Beck, Lewis C. Report of the State Geologist & Paleontologist. Albany: New York State Museum, 
1841, p.l3. 

' A Report on the Coke and Building Stone Industries in the United States, Tenth Census of the United 
States, v.lO. Washington: Government Printing Office, 1884, p. 135. 

" Ammann & Whitney, Technical Report B-Exterior Survey. A Report on the Reconstruction & 
Improvements for the New York County Courthouse, 1981, p. 2. 



Historical Background Page 36 

The stone's properties as a building material were widely praised, although, as 
early as 1841, the shortcomings of Westchester marble were evident. Beck observed in 
his report to the State Assembly that year, 

. . .the Eastchester Quarries are said at present to furnish the best material-The 
marble from these has a more compact structure, and it is stronger and more 
durable than that from other quarries. ..The objection to some of the other marbles 
from the county is, that in consequence of their friable character, they absorb 
water largely and hence, during the winter, they crumble and are defaced. ^^ 

Tuckahoe marble was considered by many to be superior to Vermont marble, Italian 

marble, and even granite. ^"^ An 185 Competition for stone to be used in the new wings of 

the United States Capitol placed Tuckahoe marble ahead of all others in compressive 

strength.^^ Thomas Ustick Walter, the architect of the Capitol expansion, was impressed 

with John Masterton's quarry and the seemingly inexhaustible supply of Tuckahoe 

marble, but the stone was eventually turned down due to its high cost. Some 25 years 

later, the U.S. Army Corps of Engineers also rated the coarsely crystalline but compact 

and durable stone ahead of New Hampshire granite and Vermont marble for compressive 

strength. ^^ 

Another boost for the Tuckahoe reputation occurred with the Boston fire of 1872. 

Tuckahoe marble structures withstood the intense heat of the blaze better than their iron 

and granite counterparts. A laboratory analysis of the Tuckahoe stone in 1887 concluded 

that it was relatively free of sulfur, iron or other constituents that might negatively 

influence its performance. ^^ John C. Smock praised the marble from Masterton's quarry 



"Beck, p. 13. 
'"'Torres, p. 14. 
'' Ibid. 
'" Ibid. 
" ibid. 



Histo rical Background Page 37 

above all others, describing it as "...coarse crystalline and pure white... buildings erected 
60 years ago show the excellent quality of this marble. "^^ 

By the mid-1880's, however, Tuckahoe marble had been in use long enough that 
the impact of weathering could not be ignored. For the Tenth Census of the United 
States, Alexis Julien catalogued the stone's decay patterns in New York City where so 
many buildings had incorporated it. The surface of the U.S. Hotel, built in 1823, showed 
one of the most characteristic signs of Tuckahoe weathering. The snowy whiteness so 
valued by early admirers had taken on a cement gray tone, and areas of the surface had 
converted into a brittle gypsum crust under which the stone continued to change to a 
powdery, grainy consistency.^^ Another characteristic of Tuckahoe weathering, surface 
pitting due to the ejection of tremolite inclusions, was evident on the U.S. Hotel as well. 
Pitting was also visible at the United States Treasury, previously the old Customs House. 
The presence of iron in the stone gave a rusty tint to many Tuckahoe buildings. More 
generally, surface crystals had simply fallen off on broad areas of building fa9ades, 
producing a rough texture. ^° The classical purity of mid-century New York had shifted to 
a decaying gray and orange thanks to the weathering of Tuckahoe marble. 

George Merrill, the Smithsonian geologist, agreed with Julien's assessment of 

Tuckahoe weathering. He noticed that. 

By exposure to the impure atmosphere of the city, its color changes to a light 
gray. This is apparently due to its coarseness of texture, which gives a roughness 
to the surface, and causes the smoke and dust to adhere to it more closely than 
they would to a finer stone. 



'"^ Smock, John Conover. Building stone in the state of New York. New York: C. Van Benthuysen & Sons, 

1888, p. 38. 

^' Julien, Alexis A. "The Durability of Building Stones in New York City and Vicinity," Tenth Census of 

the United States, v. 10. Washington: Government Printing Office, 1884, p. 366 

'°Ibid. 

*' Merrill, George E. "The Collection of Building and Ornamental Stones in the U.S. National Museum: a 

handbook and catalogue," in Annual Report of the Board of Regents of the Smithsonian Institution, showing 



Historical Background Page 38 

Merrill's observation points to the basic texture and structure of Tuckahoe marble as key 

components of its decay. Once a dressed and finished surface was weathered, the large 

grains facilitated the settling of particulate matter and the introduction of moisture and 

salts to the interior of the stone. 

Julien went beyond describing stone weathering to try to understand its root 

causes. In the Tenth Census, he noted that the behavior of marble in urban environments 

could not be explained simply by moisture content, as was commonly accepted at the 

time. Rather, the peculiarities of texture as determined by metamorphism could explain 

far more about marble weathering. On the bending of marble he wrote, 

...the irregular and closely contiguous grains of calcite which make up a white 
marble are united by no cement, and have apparently a very feeble coherence. It 
appears to me probable also that their contiguous crystallization has left them in a 
state of tension, on account of which the least force applied, through pressure 
from without, or of the unsupported weight of the stone, or from thermal 
expansion by heat or frost, produces a separation of the interstitial planes in 
minute rifts. Such a condition permits a play of the grains upon each other and 
considerable motion... In such cases, also, I have observed that the mutual 
attrition of the grains has been sometimes sufficient to convert their angular, often 
rhomboidal, original contours into circular outlines, the interstices between the 
rounded grains being evidently filled up by much smaller fragments and rubbed 
off particles. " 

Later, when discussing tension and loss of cohesion between grains within a stone, Julien 

refers to Tuckahoe marble: 

A crystalline building stone... is made up almost entirely of imperfect crystals of 
its constituent minerals... closely compacted together, originally with intense 
mutual pressure. Sometimes no cement intervenes. . .Such a condition must be 
sensitive to very slight influences, the surfaces of the grain in a building 
alternately pressed still more tightly together or separated to disruption, e.g. by 
variations of temperature... A good illustration is found in those marbles which 
seem to contain no cement in their interstices, e.g. the coarse Tuckahoe marble, 
which soon becomes seamed with cracks. " 

the operations, expenditures, and conditions of the institution for the year ending June 30, 1886, Part II. 
Washington: Government Printing Office, 1889, p. 380. 
*■ Julien, p. 367. 
*^ Ibid., p. 379. 



Historical Background Page 39 

Julien's observations highlight the primary role of microstructure in the weathering of 

marble. The issues he discussed in the Tenth Census continue to shape our understanding 

of stone decay. The relationship between cyclical heating and cooling and the 

deformation of marble at the level of the individual grain boundary is essential to the 

behavior of both Tuckahoe and Sheffield marbles. Julien did not mention the Tweed 

Courthouse in his survey, but the patterns of decay exhibited so early in the building's 

life are characteristic of Tuckahoe marble. 

Where much has been written about Tuckahoe marble, far less is known about 

Sheffield marble. The quarries of Berkshire County had provided stone locally since at 

least the first half of the 19"^ century. The only other known use of Sheffield marble on a 

large-scale was in the Washington Monument in Washington, D.C. George Merrill 

mentions the Sheffield quarry in connection with the quarry in Lee, Massachusetts 18 

miles to the north. Lee marble had been used in the extensions to the United States 

Capitol and was relatively well known. Merrill writes. 

Crystalline limestones and dolomites of such a character as to assume the name of 
marble are now or have been in times past quarried in various towns of Berkshire 
County, in this state. The stones are all white or some shade of gray color, 
medium fine-grained in texture, and are better-adapted for general building than 
for any form of ornamental work... In the quarries the stone lies very massive, and 
it is stated cubes 20 feet in diameter could be obtained if necessary. The Sheffield 
quarries were opened in 1838. The rock there is massive, with but little jointing. 
Natural blocks 40 feet square can be obtained. 

It is not certain that the Berkshire marbles are in fact dolomitic, as Merrill believed. 
However, on the other accounts Merrill's observations are worth noting. The fine- 
grained texture of the Berkshire County marbles is one of their defining characteristics, 



^ This is based on a conversation with the owner of the former Briggs quarry, who claims to have 
documentation provided by the National Park Service. It is not independently verified. 
^' Merrill, p. 379. 



Historical Background Page 40 

and like the Tuckahoe marble, accessory minerals were another defining characteristic. 

Merrill writes that much of the stone from the Berkshire quarries contained small crystals 

of yellowish tremolite. The tremolite crystals tended to weather out of the surface within 

a few years, leaving a pock-marked appearance. This behavior was visible in the 

exterior walls of the Capitol building even in Merrill's day. 

John Strong Newberry's description of the Lee quarry was included in the Tenth 

Census, and it provides more information on some of the important features of Berkshire 

marble. Again like the Tuckahoe, Berkshire marble typically contained a noticeable 

amount of iron and visible inclusions. He wrote. 

The Lee marble is for the most part of uniform though not brilliant white color, is 
coarser grained than the Vermont marbles, and yet finer than those of New York. 
It is a strong and durable stone but contains a little iron, by the oxidation of which 
it becomes somewhat brown on exposure. It is doubtful whether its strength and 
durability are materially impaired by this, and the change of color which it 
produces is by some architects regarded as an excellence rather than a defect. It 
usually contains a little pyrites, but it is a remarkably white marble. 

The existence of these four features, magnesium content, iron content, tremolite and 

pyrite inclusions, and general white coloration, indicates the degree of relatedness 

between Tuckahoe marble and Sheffield marble. Similar geological provenance accounts 

for this relatedness. Although the Westchester and Berkshire county quarries are 

separated by over 100 miles, the stone they produced during the years of their greatest 

activity was strikingly similar. It is useful to remember this fact when considering the 

variation in decay that manifested itself at the Tweed Courthouse over time. 

While the two types of marble used in the construction of the Tweed Courthouse 

derive from a single geological formation, the individual characteristics of texture, grain 



^ Ibid. 

A Report on the Coke and Building Stone Industries in the United Stales, p. 323. 



Historical Back ground Page 41 

boundary, grain size and grain shape unique to each type of stone have produced 
observable differences that are as striking as their similarities. Despite their undeniable 
relatedness, Tuckahoe and Sheffield marble exhibit distinct patterns of weathering that 
derive from the idiosyncrasies of mineral composition and micromorphology. These 
patterns of weathering will be discussed in the following chapters. 



CHAPTER III 
Previous Analysis and Cleaning 

Although their formal results have never been published, several investigations of 
the Tweed Courthouse marble have been performed within the past twenty years. The 
first significant tests, which applied x-ray diffraction (XRD) and scanning electron 
microscopy (SEM) to a group of 24 samples taken from the south side of the building, 
occurred in 198 1.*^^ In 1989, as a preliminary step in determining a suitable method for 
cleaning the exterior marble, 16 stone samples were observed under an optical 
microscope, and SEM and Energy-Dispersive X-Ray Microanalysis (EDXA) were 
performed. ^^ Subsequent to this analysis, cleaning tests were performed and a method 
was chosen for cleaning the marble. In 1991, further testing was performed in order to 
determine an appropriate conservation treatment for the extensively deteriorated 
marble. ^° Three drilling cores were chosen to represent the exterior marble and were 
used for XRD and a wide array of laboratory tests. Finally, as part of the current 
restoration, another round of surface cleaning was implemented in 2000. This took place 
ten years after the first cleaning. In order to understand what is and is not already known 



A Report on the reconstruction and improvement to the New York County Courthouse 
(Tweed Courthouse). Prepared by Ammann & Whitney, Consulting Engineers and Beyer, Blinder, Belle, Architects 
and Planners. New York, February 1981. 

*' Rehabilitation and restoration of 52 Chambers Street (Tweed Courthouse), Borough of Manhattan, City of New 
York, for the Department of General Services, PW-292-01. Prepared by Mesick, Cohen, Waite Architects. Albany, 
1989. 

Evaluation of Submitted Masonry Samples: Recommendations for Conserxation Treatment. Tweed 
Courthouse, 52 Chambers St.. New York. NY. Project No. 9010-38 MSSC. Prepared for Mesick, Cohen, Waite 
Architects by the Stone Testing Laboratory, Masonry Stabilization Services Corporation. March 1991. 

42 



Previous Analysis and Cleaning Page 43 

about the Tweed Courthouse marble, it is worthwhile to examine the results of these 
different testing programs. 

1981 Exterior Survey by Ammann & Whitney 

In 1981, engineers from the firm of Ammann & Whitney consulted with the 
architectural firm of Beyer Blinder Belle to produce an exterior survey of the Tweed 
Courthouse for the Department of General Services, the agency that oversees New York 
City's government buildings. The purpose of the report was to provide a 
recommendation for the rehabilitation of the courthouse, which by the late 1970's had 
become a source of concern. Figures 3.1 and 3.2 give some indication of the condition of 
the building's exterior. Decaying marble on the columns and in the cornice created a 
serious falling hazard for city employees and pedestrians in City Hall Park. Ammann & 
Whitney Consulting Engineers was asked to determine why the stone was failing and 
what could be done to repair it. During the course of their work, vibration from a coring 
drill did in fact cause a large carved leaf of a column cap to detach and fall, confirming 
concerns about the extent of the decay. 

Technical Report 'B '-Exterior Survey includes the findings of the chemical and 
mineral analyses performed as part of this investigation. For the purposes of testing, 
Ammann & Whitney took 24 marble and mortar samples from the south side of the 
building. Some samples were removed from the Eidlitz addition but most were taken 
from the Kellum portion of the building and all were within reach of a stepladder or open 
window. Each sample was subjected to XRD and examined using SEM. 



Previous Analysis and Cleaning 



Page 44 




Figures 3.1 & 3.2: Discoloration on the north facade, east and west sides of the portico. May, 1989. 



Ammann & Whitney were able to calculate exact proportions of constituent 
minerals using XRD. This was apparently accomplished by fine-tuning the machine in 
the laboratory to provide precise readings. Of the 2 1 marble samples tested, it was found 
that 1 1 had a dolomite content of 76% or greater. Of those samples, the micaceous 
mineral phlogopite accounted for 10% or more in 2 samples and was present as a minor 
accessory mineral in the other 8. It was also found that quartz was a major component 
(49%) in one sample and a minor component in 8 others. Calcite was present as an 
accessory mineral in 6 of the 1 1 dolomitic samples.*" 

In the 10 calcitic samples, calcite content ranged from 72% to 95%. Phlogopite 
was an accessory mineral in 5 samples and in 2 of those it comprised 10% of the total. 



Ammann & Whitney, pp. 15-37. 



Previous Analysis and Cleaning Page 45 

Muscovite and quartz were also present. Quartz appeared in 8 samples, and in two 
samples it made up 7% and 10% of the total. A breakdown of test results is given in 
Table 1. 

The frequent appearance of quartz and phlogopite in both categories of stone is 
significant. Ammann & Whitney concluded that the presence of micaceous phlogopite 
was one reason for the patterns of deterioration visible on much of the exterior. Where 
the sheety mica inclusions were close to the surface, they acted as a wick for moisture 
and in freezing weather led to rapid removal of surface material.^" This phenomenon was 
discussed by Lewin and Charola in 1981.'^ Phlogopite, which originally may have been 
valued for the sparkling appearance it gave to the stone, was the most likely source of the 
commonly observed "pock-marking" of the surface. The significance of quartz was not 
mentioned, but it may account for some lack of cohesion within the marble. The 
engineers also noted iron oxide staining and attributed this to the leaching of ferruginous 
minerals such as pyrite within the stone or to rusting of metal on the outside of the 
building. 

The most interesting outcome of the 1981 Exterior Survey was the new 
understanding it prompted about composition of the marble used to build the Tweed 
Courthouse. It had long been assumed that marble from both quarries was dolomitic. On 
the contrary, tests showed that calcitic marble accounted for 1/3 or more of the exterior 
stone. Based on the textural and compositional range observed by Ammann & Whitney, 
it was felt that as many as seven different quarries could have provided the stone. Yet the 
two broad categories drawn by the tests, calcitic and dolomitic, indicated the possibility 



^- Ibid., p. 12. 

^"' Lewin, Seymour Z. and A. Elena Charola, "Stone decay due to foreign inclusions." Preprints of the Contributions 

to the International Symposium on the Conservation of Stone; Part A, Deterioration, Bologna, 1981. 



Previous Analysis and Cleaning Page 46 

of two general locations for the quarrying of the stone. Since the Westchester marbles 
are widely classified as dolomitic, it is reasonable to assume that the Sheffield quarry was 
the source of the calcitic marble sampled. Ammann & Whitney did not interpret their 
results this way, but the patterns of decay observed prior to the two cleaning campaigns 
could be explained in part by the behavior of two general types of marble deriving from 
two general locations. 

Supporting this observation is the detection of another mineral in the XRD 
analysis performed by Ammann & Whitney. Calcium sulfate or gypsum (CaS04- 
2H2O) was observed in nearly half of the samples. The presence of gypsum can be 
attributed in part to the sampling technique employed, which relied on surface scrapings 
or included portions of surface material for use in XRD. The process of formation of 
gypsum from the interaction between calcium and sulfur is well known. Sulfation is to 
be expected in exterior marble subjected to an urban climate; but because magnesium is 
slower to react with sulfurous compounds than calcium in solution, the occurrence of 
gypsum is less common on dolomitic marble than it is on calcitic marble. This was true 
in the tests performed by Ammann & Whitney. Gypsum was present in 9 of the 21 
samples; of those 9 samples, 8 were calcitic marbles. In one of these 8 samples, gypsum 
accounted for 12% of the total, the rest being calcite. Results of the XRD tests are 
summarized in Table 3.2. 

In their conclusions, Ammann & Whitney comment on the role of gypsum and the 

absorption of soluble salts in the decay of exterior marble at the Tweed Courthouse: 

The other main source of ongoing decay is due to the attack of acidic air 
pollutants (oxides of sulfur and nitrogen from combustion of fossil fuels and 
automotive vehicle exhausts.) These react with the alkaline stone (dolomitic and 
calcitic marble), eroding it and producing soluble salts (gypsum) that, under the 



Previous Analysis and Cleaning 



Page 47 



influence of normal wet-to-dry cycling, undergo internal migration and 
recrystallization, and produce the characterisitc manifestations of "salt-decay." 

If this is the case, it may be possible to make a finer distinction between the samples 

analyzed. Based on the data obtained by XRD, it could be stated that surface decay due 

to the recrystallization of soluble salts is more likely to be observed in the calcitic marble 

than in the dolomitic marble. If a connection between provenance and composition, i.e. 

between location (Tuckahoe, New York versus Sheffield, Massachusetts) and 

classification (calcitic versus dolomitic), can be confirmed, then this observation takes on 

greater significance for the characterization of decay mechanisms in the two types of 

stone used at the Tweed Courthouse. Since a piece of calcitic Sheffield marble would be 

more likely to have a surface formation of calcium sulfate than a piece of dolomitic 



Number 


Calcite 


Dolomite 


Phlogopite 


Quartz 


Gypsum 


Muscovite 


Location 


Type 


1 


82% 


0% 


10% 


minor 


minor 


minor 


l<nown 


calcitic 


2 


minor 


93% 


minor 


0% 


minor 


0% 


hcnown 


dolomitic 


3 


0% 


96% 


minor 


minor 


0% 


0% 


l<nown 


dolomitic 


4 


0% 


89% 


10% 


minor 


0% 


0% 


known 


dolomitic 


5 


86% 


0% 


0% 


7% 


0% 


0% 


known 


calcitic 


6 


0% 


51% 


0% 


49% 


0% 


0% 


known 


dolomitic 


7 


minor 


76% 


20% 


minor 


0% 


0% 


known 


dolomitic 


8 


minor 


90% 


minor 


minor 


0% 


0% 


known 


dolomitic 


9 


0% 


96% 


minor 


minor 


0% 


0% 


known 


dolomitic 


10 


minor 


92% 


minor 


minor 


0% 


0% 


known 


dolomitic 


11 


72% 


0% 


10% 


12% 


minor 


minor 


known 


calcitic 


12 


95% 


0% 


0% 


0% 


minor 


0% 


known 


calcitic 


13 


95% 


0% 


0% 


0% 


minor 


0% 


known 


calcitic 


14 


86% 


0% 


0% 


minor 


12% 


0% 


known 


calcitic 


15 


86% 


0% 


minor 


minor 


minor 


minor 


known 


calcitic 


16 


minor 


89% 


minor 


minor 


0% 


0% 


known 


dolomitic 


17 


94% 


0% 


minor 


minor 


0% 


minor 


known 


calcitic 


18 


minor 


91% 


minor 


minor 


0% 


0% 


known 


dolomitic 


19 


0% 


95% 


minor 


0% 


minor 


0% 


known 


dolomitic 


20 


87% 


0% 


minor 


minor 


minor 


minor 


known 


calcitic 


21 


92% 


0% 


minor 


minor 


minor 


minor 


known 


calcitic 



Table 3.1: Mineralogical constituents detected using X-Ray Diffraction. Ammann & Whitney, 1981. 



Previous Analysis and Cleaning Page 48 



Tuckahoe marble, this difference should be visually evident to some degree. And on the 
dolomitic marble, a highly soluble, highly hygroscopic gypsum-epsomite 
(MgS04-7H20)-- would be expected to form. 



1989 Cleaning of the Exterior Masonry: Pre-preliminary Report 
by Mesick, Cohen, Waite, Architects 



Eight years after these tests, the Albany-based firm of Mesick, Cohen, Waite 
Architects (MCWA) was hired by the Department of General Services to produce a 
comprehensive feasibility study for the restoration of the Tweed Courthouse. The first 
part of that study involved a preliminary analysis of the masonry and the execution of 
small-scale cleaning tests. A few sections of scaffolding were erected on the exterior, but 
samples were obtained and tests were carried out mostly on areas that could be reached at 
ground level. For their laboratory analysis, MCWA consulted with the Environmental 
Particulates Analysis at the Atmospheric Sciences Research Center of the State 
University of New York at Albany. Testing again involved SEM, but instead of using 
XRD for the identification of constituent minerals. Energy Dispersive X-Ray 
Microanalysis (EDXA) was applied to each sample while in the scanning electron 
microscope. EDXA identifies elements rather than mineralogical composition, and 
results are not reported as percentages of the entire sample. 16 samples were taken from 
the building and locations for these samples were not noted. Between 5 and 12 locations 
on each sample were tested with EDXA. Averaged compositions of test locations on 



Previous Analysis and Cleaning 



Page 49 



Number 


Mg 


Al 


Si 


P 


S 


CI 


K 


Ca 


Fe 


Location 


Type 


1 


high 


none 


high 


ow 


ow 


none 


none 


high 


ow 


unknown 


dolomitic 


2 


high 


none 


high 


ow 


ow 


none 


none 


high 


ow 


unknown 


dolomitic 


3 


high 


none 


high 


ow 


ow 


none 


none 


high 


low 


unknown 


dolomitic 


4 


ow 


high 


high 


none 


none 


none 


none 


high 


high 


unknown 


calcitic 


5 


high 


none 


high 


low 


low 


none 


none 


high 


low 


unknown 


dolomitic 


6 


V. low 


V. low 


low 


none 


none 


none 


V. low 


high 


low 


unknown 


calcitic 


7 


high 


none 


low 


low 


low 


none 


none 


high 


high 


unknown 


dolomitic 


8 


none 


V. low 


low 


none 


none 


none 


V. low 


high 


V. low 


unknown 


calcitic 


9 


none 


low 


high 


none 


none 


none 


low 


none 


low 


unknown 


inclusion 


10 


high 


none 


high 


low 


low 


none 


none 


high 


V. low 


unknown 


dolomitic 


11 


high 


none 


high 


low 


moderate 


none 


none 


high 


V. low 


unknown 


dolomitic 


12 


high 


none 


high 


low 


moderate 


none 


none 


high 


V. low 


unknown 


dolomitic 


13 


low 


none 


none 


none 


none 


none 


none 


high 


low 


unknown 


calcitic 


14 


low 


low 


moderate 


low 


low 


low 


low 


moderate 


moderate 


unknown 


uncertain/ 
calcitic 


15 


none 


low 


high 


low 


none 


low 


none 


high 


low 


unknown 


calcitic 


16 


high 


none 


high 


low 


moderate 


none 


none 


high 


low 


unknown 


dolomitic 



Table 3.2: Elements detected using EDXA. Mesick, Cohen, Waite, 1989. 

each sample are given in Table 3.2. Samples were also observed under an optical 
microscope with photomicrographic dispersive staining capability. 

The results of these tests were less precise than the 1981 tests, but they tend to 
confirm the earlier findings. 9 of the samples can be characterized as dolomitic marble 
based on the presence of calcium and magnesium, and 6 can be characterized as calcitic 
based on the presence of calcium and the absence or very low presence magnesium. One 
sample appeared to be an inclusion of pure silicon and another sample, grouped for 
simplicity with the calcitic marbles, had more silicon than calcium. Other chemicals 
present were sulfur, silicon, chlorine, iron, phosphorus, and titanium. 

Sulfur was present on the surface or interior of 9 of the samples. 7 of these were 
dolomitic marble. Although it is impossible to infer from EDXA if this indicates the 
presence of calcium sulfate, MCWA considers this to be proof of gypsum formation on 



Previous Analysis and Cleaning ^ ^"^^ ^^ 

the dolomitic marble samples.^'' It could also be interpreted to mean that sulfurous 
particulate matter, and not gypsum, was more common on large exposed surface grains of 
the dolomitic marble or that magnesium sulfate (MgS04) was present. 

h-on was present in 7 of the dolomitic samples and in 2 of the calcitic samples. 
The presence of iron is significant for weathering, although again it is impossible to say 
with certainty why it is present. In analysis of sample 1, MCWA writes that the iron 
detected in the dolomitic marble indicates the presence of hornblendes, but elsewhere the 
presence of iron is attributed to the deposition of fly ash on the surface of the stone. It 
may also be due to the presence of pyrite. Iron has been observed in Tuckahoe marble 
from other buildings, so this may be an accurate assumption for the dolomitic marbles. It 
is likely that the iron observed using EDXA is a combination of existing iron content and 
iron deposited in the form of fly ash or other pollution, as stated by MCWA. 

Another element observed using EDXA was silicon. Silicon was detected in 1 1 
samples and was the dominant constituent in 1 of these. This can be explained by the fact 
that various silicates and silico-aluminates are usually present in these marbles. 
Phosphorus was present as a result of a bird-proofing agent applied to many of the ledges. 
The chemicals sulfur and chlorine were also observed in some of the samples, indicating 
the presence of salts within the stone and the influence of atmospheric pollutants. Carbon 
particles could account for some of the surface yellowing seen in much of the stone. 

The characterization of stone samples performed by MCWA for their report to the 
Department of General Services served the larger purpose of helping to determine a 
proper method of cleaning the exterior marble. 19 tests were performed on isolated areas 



'" Rehabilitation and Restoration of 52 Chambers Street (Tweed Courthouse). Borough of Manhattan. City of 
New York, for the Department of General Services. PW-292-0L Prepared by Mesick, Cohen, Waite Architects, 
Albany, 1987, Appendix B. 



Previous Analysis and Cleaning Page 51 

of the building. The difference between soiled and cleaned surfaces was, in most of the 
tests, dramatic. Figures 1 and 2 show the degree of color change between soiled and 
cleaned stone. They provide an inkling of the original whiteness of the Tweed 
Courthouse in its earliest days. After testing everything from crushed walnut shells to 
water soaking, MCWA recommended a three-step process for cleaning the building. " 
Step one involved removal of the pigeon proofing substance using a metal scraper. Step 
two involved pressure rinsing the stone with water at a pressure of 500 psi and with a fan 
tip nozzle of at least 40 degrees. The third step required the brushed application of an 
alkaline prewash such as Prosoco's Sureklean 766" to the surface with a dwell time of 30 
to 60 minutes. Dwell time varied according to the seriousness of surface soiling. After 
the appropriate dwell time, the prewash was to be rinsed off. The fourth step called for 
application of an afterwash, such as Sureklean Retoration Kleaner®, which should be 
pressure rinsed after 5 minutes. The final step was to test the surface for pH to ensure that 
the chemicals had been thoroughly removed. 

In addition to their recommendation for cleaning, MCWA also commented on the 
general conditions of decay that they observed on the building. By 1989, many of the 
architectural details that were most exposed to wind, rain, sun, and freezing had seriously 
decayed or simply fallen off, like the abacus details of many of the capitals. Areas 
especially susceptible to damage and staining were the column and pilaster flutes, 
window trim, and rusticated blocks on the first floor. 

Because their test results corroborated the existence of two different types of marble on 
the exterior of the building, MCWA observed the behavior of the marble with this in 



" Ibid., p. 38. 
"' Ibid., p. 20. 



Previous Analysis and Cleaning P^g^ ^^ 

mind. The "two types of marble," as MCWA called them, seemed to be weathering 
differently, although they did not identify the difference as deriving from the original 
quarry location. The stones were referred to simply as "gray" and "white."^^ Most of the 
fagade was made up of the "dark gray" stone, and the rest was made up of "quite white" 
stone. In the gray stone, numerous small holes were evident where hard mineral 
inclusions had fallen out. This is in keeping with Julien's description of Tuckahoe 
marble. The holes themselves were stained yellow or brown, suggesting that the 
inclusions contained iron.*^^ All of the stone in the Eidlitz wing was dark gray prior to 
cleaning. This would seem to confirm the sameness of the gray stone and the Tuckahoe 
marble, also indicated by the construction timeline. It was also remarked that the stone in 
the Eidlitz wing seemed to be in better condition than the stone in the Kellum section of 
the building. This suggests that the Tuckahoe is in general a more sturdy material than 
the Sheffield. 

In contrast, the "white" blocks had relatively smooth surfaces without holes or 
inclusions, and dark yellow/brown stains were common in areas that were not washed by 
water. This may be due to surface gypsum trapping fly ash and other particles. Such a 
pattern is in keeping with Newberry's description of Lee marble in the Tenth Census. 
Some sections of both the white and gray stone were so friable that they simply turned to 
"marble sand" when touched. 

The report to the Department of General Services also describes patterns of black 
crust formation on the exterior stone. In areas of the fa9ade protected from the flow of 
water, particularly the moldings at the sides of the windows under lintels and segmental 



'' Ib.d. 
"'Ibid. 



Previous Analysis and Cleaning 



Page 53 




Figure 3.3: Cleaning test number 10 performed on two blocks of Tuckahoe marble at the first floor 
level, July 1989. 




Figure 3.4: Close-up of cleaning test number 10. Gray discoloration and pock-marking are evident. 



Previous Analysis and Cleaning .^ Page 54 

pediments, and the joints in the rusticated blocks at the first floor, gypsum crusts were 
common. These crusts were extremely friable and could be removed by hand. 

1991: Evaluation of Submitted Masonry Samples 
by Masonry Stabilization Services Corporation 

Mesick, Cohen, Waite's contract with the Department of General Services also 
called for testing of possible consolidants. Since the stone would continue to decay 
regardless of cleaning, it was considered important to review treatments that might at 
least slow this process. MCWA hired Masonry Stabilization Services Corporation 
(MSSC) of Kansas City to carry out these tests. In order to quantify how the stone would 
perform before and after treatment, the Stone Testing Laboratory at MSSC analyzed 
some of the traits of the stone, including hygroscopic moisture uptake, water absorption, 
acid solubility, water solubility, anionic salt content, accelerated weathering, and 
measurement of color change. All of these tests were performed according to ASTM 
standard methods. 

Following the lead of MCWA's previous report, three basic categories of stone 
were created. Category 1 was labeled "white marble," category 2 was labeled "gray 
marble," and a third category labelled "Type 01" was also included. It is not clear what 
the term Type 01 refers to, although it must have been relatively common. 

The samples themselves were cut to uniform sizes (2" diameter by 1-1/2" length) 
from cores drilled to depths greater than 2 feet in the exterior walls. 6 of each type of 
sample were obtained. All of the stone was recorded to be in sound condition. XRD 



Previous Analysis and Cleaning 



Page 55 



results are provided in Table 3.3, and the basic properties of the three substrates are 
summarized in Table 3.4. 

MSSC also performed XRD and basic observation under an optical microscope 
for all of the samples. This revealed that the Type 01 samples were a white marble 
composed chiefly of calcite with minor amounts of dolomite.^^ It was noted that the 
substrate was almost pure calcite with no traces of other minerals. Minor amounts of 
dolomite were detected, and average grain size was observed to be 0.5mm. From this 
description, Type 01 matches samples of the Sheffield marble analyzed in Chapter 4. 

The gray marble was characterized as a dolomitic marble composed primarily of 
dolomite with small amounts of calcite. "^° The crystals were large, measuring up to 
several millimeters in diameter. Abundant small flakes (about 0.5mm wide) of 
magnesian mica, or phlogopite, were present, and pyrite was noted to be abundant. 
Graphite and wollastonite may have been detected, but the identity of these minor 



Sample 


X-Ray Diffraction Mineralogical Summary 


Major 


Minor 


Trace 




Type 01 


calcite dolomite none 




Gray Marble 


graphite, wollastonite?, 
dolomite, pyrite phlogopite, hydromica kaolinite? 




White Marble 


dolomite, phlogopite calcite pyrite, qypsum 





Table 3.3: Mineralogical constituents detected using X-Ray Diffraction. MSSC, 1981. 



99 



Evaluation of Submitted Masonry Samples; Recommendations for Conserx'ation Treatment. Tweed 
Courthouse. 52 Chambers St.. New York. NY. Project No. 9010-38 MSSC. Prepared for Mesick, Cohen, Waite 
Architects. Prepared by the Stone Testing Laboratory, Masonry Stabilization Services Corporation, March 



1991, p. 13. 
"^ Ibid. 



Previous Analysis and Cleaning 



Page 56 



accessory minerals is not certain in the XRD readout provided in MSSC's report. 
Judging by the other characteristics, the gray marble is a close match for Tuckahoe 
marble. 

Compositionally similar to the gray marble, the white marble was described as a 
white dolomitic marble comprised chiefly of dolomite and phlogopite with low amounts 
of calcite."^' The phlogopite grains were several millimeters large and oriented parallel 
to each other. Pyrite was present in traces, as was gypsum. The tested samples are not 
accompanied by photographs, and no locations are given for the samples, making it 
impossible to visually cross-reference MSSC's results with other stone from the building. 



Sample 


24 Hr. Water 
Absorption, 

%wt 

ASTM C 97 


Anionic 

Salt 

Content 


Surface pH 


Hygroscopic 

Moisture 

Uptake 

(48hrs.at94% 

RH) 


Solubilities 

of Untreated Samples 


Chloride 
01- 


Sulfate 
S04- 


Nitrate 
N03- 


Water 
Soluble 
Content 
%Wl 


Acid 

Soluble 

Content 

%wt 


1 


Type 01 0.14% <30 ppm <50 ppm 


<1 ppm 


6.96 to 8.45 


0.00% to 0.05% 


2.02% 


92.50% 




Gray Marble 0.16% <30 ppm <50 ppm 


<1 ppm 


8.61 to 8.72 


0.01% to 0.08% 


0.00% 


91.50% 




Wliite Marble 0.23% <30 ppm <69 ppm 


<1 ppm 


7.98 to 8.47 


0.00% to 0.09% 


0.00% 


91.00% 





Table 3.4: Basic properties of three marble types. MSSC, 1991. 



Ibid. 



Previous Analysis and Cleaning 



Page 57 



W- 




1 j^ ^ A # j^ 1 4flH 


r-T-T-^^^"^^ 


1" 


■1 



Figure 3.5: Tuckahoe marble balusters showing extreme degradation due to weathering. 
Characteristic gray discoloration and blackening from the accretion of pollutants are evident. 
Projecting elements of both types of marble tend to look alike because of pollution staining. Photo 
taken May, 1989. 



Observations about Exterior Weathering 



Subsequent to MCWA's testing, no further analysis was performed on marble 
samples from the Tweed Courthouse. Thorough cleaning was undertaken using the 
recommendations made by Mesick, Cohen, Waite Architects and the courthouse was 
returned to a state of relatively uniform whiteness, removing the most obvious visual 
clues of differential weathering. Cleaning was undertaken again in 1999 prior to the 
Economic Development Corporation's current restoration. Without being able to refer to 
the building itself as a general gauge of comparative weathering as it is manifested in 
surface discoloration and the accretion of pollutants, it is difficult to make observations 
on the weathering of the two types of marble. Even so, the building provides a wealth of 
information about the behavior of Sheffield and Tuckahoe marble. 



Previous Analysis and Cleaning Page 58 

The collection of photographs taken by MCWA as part of their work there 
provides the best record of the conditions of decay that existed on the building prior to 
cleaning. After an analysis of MCWA's photographic archive of the previous conditions 
on the building, the following observations were made: 

1) The gray stained marble shows the characteristic properties of Tuckahoe 
marble: medium to large grain size, gray surface deposition of sooty pollutants and 
gypsum crust formation on projecting elements (See Figure 3.5.) Surface friability is 
often extreme. Figure 3.6 and 3.7 show that in areas where the stone is thin, it has 
detached from the substrate. Small iron spots are also visible on many of the elements, as 
shown in Figure 3.8. The graying of Tuckahoe marble is likely to be an urban 
phenomenon, since Tuckahoe samples on the Stone ExposureTest Wall at the National 
Institute of Testing and Standards in rural Maryland have not become gray in 50 years of 
exposure (see Figure 3.9.). 

2) Reddish iron-stained marble is mixed in with the gray marble on most of the 
fagade (see Figure 3.10.) As with the gray marble, black crusts had covered the most 
exposed elements of this type of stone, making it difficult to differentiate even when 
severely decayed. On the south facade of the east pavilion of the Kellum section, severe 
iron staining is visible across the entire surface (see Figure 3.1 1). Similar iron staining is 
common in a sample of stone from Lee, Massachusetts at the NIST (see Figure 3.12). In 
one instance, a ledge-like window hood was coated with bird-proofing material, causing 
moisture to be trapped inside the stone and intensifying iron staining and decay 
(Figure3.13.) This seems to indicate the leaching of ferruginous minerals such as pyrite. 
The prevalence of iron staining in this area may be attributable to the prevalence of 



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P age 5 9 





Figures 3.6 & 3.7: Chipped pilaster flutes to the left and a chipped rusticated basement block to the 
right. Many of the finer details of the Tuckahoe marble have detached due to weathering. The 
whiter substrate has been exposed, revealing the level of discoloration. Photos taken May, 1989. 




Figure 3.8: Leaf detail with degraded surface show ing exposed individual grains and iron stains. 
Weathering has made the surface extremely friable. Photo taken August 2000. 



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Page 60 




Figure 3.9: A smooth but slightly iron-stained sample of Tuckahoe marble in the Stone Exposure 
Test Wall at the NIST. After 50 years of exposure, no gray discoloration was visible. The large 
grains are highlighted by the reflection of the sun on the surface. 




Figure 3.10: Iron-stained marble, probably Sheffield, interspersed with blocks of Tuckahoe. Iron 
staining may be due to the leaching out of ferruginous minerals such as pyrite. Note how the stone 
has been washed white in areas of rain runoff near the Tuckahoe marble while the Tuckahoe has 
remained a solid gray color. Photo taken May, 1989. 



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Page 61 



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Figure 3.11: South facade, west end. May, 1989. Extreme staining is visible across tlie entire surface. 
This type of discoloration is typical of Lee marble, a stone quarried within 20 miles of Sheffield, MA. 
The south facade exhibits the worst weathering on the building. 




Figure 3.12: An iron-stained sample of Lee marble in the Stone Exposure Test Wall at the NIST. 
Like the Tuckahoe sample, discoloration due to pollution was not noticed. 



Previous Analysis and Cleaning 




Figure 3.13: A Sheffield window header that had been covered with bituminous bird-proofing. The 
corner shows the effects of trapped moisture. This part of the stone could be removed merely by 
scraping the surface. 




Figure 3.14: A combination of blackening and iron-staining on the left is non-existent on the right of 
these two blocks in the center of the photograph. The Similar to the iron-stained blocks, rain runoff 
appears to be washing part of the surface. 



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Page 63 




Figure 3.15: Exposed areas where moisture is likely to collect, such as the cornice, show the most 
intense staining and decay. 

Sheffield stone and to the microcHmate of this section of the building. 

3) Elsewhere, the same type of stone appears to be an "unstained" white color. 
The white is often side by side with black staining on the same piece of stone. This may 
simply be a less iron rich version of the previously described stone. A factor that 
appears to affect the relative cleanness of all of the exterior stone at the Tweed 
Courthouse is the amount of runoff across the surface of the building (see Figure 3. 14). In 
the case of the white stone, areas that are regularly washed by rainwater seem to be 
cleaner than other areas where moisture may linger and not evaporate, like the cornice 
area shown in Figure 3. 15. Unwashed locations are prime for the conversion of sulfurous 
particulates into gypsum and the initial migration of soluble salts into the stone. 

4) Visual distinction between what appear to be the Sheffield and Tuckahoe 
blocks, based on the observed weathering properties, was easily made prior to cleaning. 



Previous Analysis and Cleaning Page 64 

Both are mixed randomly, and even close proximity did not make the weathering more 
uniform. Figure 3.16 shows the typical juxtaposition. 

5) Gypsum formation in especially exposed areas of the balustrade and cornice, 
produced hardened surface crusts beneath which water infiltration and freeze-thaw 
cycling continued to act on sound stone. This is evident in Figure 3.17. Both types of 
stone seem to have been affected by this phenomenon in very exposed locations. 

Drawing on the facts of the Tweed Courthouse's construction, the historic 
accounts of both types of stone, and the observations of testing in the past 25 years, 
general characterizations of the Tuckahoe and Sheffield marble can be made. The 
Tuckahoe can be expected to weather to a dull gray, crack and break off in especially fine 
detailing, and exhibit pocking and iron staining in some areas. When the original dressed 
and finished surface of ornamental stone has weathered a few millimeters, the large 
grains become exposed and extremely friable. This characteristic texture is visible in 
Figure 3.2. The finer-grained Sheffield marble can be expected to acquire a reddish hue 
or extreme blackening when it weathers. In areas where the surface of the Sheffield stone 
is washed by water, especially by runoff from the magnesium rich Tuckahoe, the stone 
may stay closer to its original pure-white color. When the surface is eroded, the loosely 
crystalline stone often turns to marble sand. Both types of marble are susceptible to 
formations of gypsum crust, but the calcitic Sheffield is more likely to suffer from serious 
decay due to calcite's faster reaction rate with airborne pollutants. 

The photographic record makes it clear that the earlier, obvious signs of 
differential weathering are no longer there to assist in the identification of Sheffield and 
Tuckahoe marble in their various locations on the building. That pronounced differences 



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Page 6 5 




Figure 3.16: This photograph illustrates the juxtaposition of different stone types that is clear today 
but which was not obvious at the time of construction. Iron-stained blocks in the wall, probably 
Sheffield marble, are visually distinguishable from the gray, discolored stone, which is probably 
Tuckahoe. The window jambs both appear to be Tuckahoe, although the one on the left is 
significantly more chipped and discolored. 



Previous An a lysis and Cleaning Page 6 6 




Figure 3.17: A modillion appears to be splitting at tlie seams due to continued freeze/thaw cycling 
beneath a hard surface crust of gypsum. Note the semicircular patterns of brownish and blackish 
iron deposits due to the diffusion of iron leachates and other atmospheric pollutants. 



in weathering did exist between certain types of stone on the exterior of the courthouse 
was not in doubt in previous rounds of analysis. However, the differences in weathering 
were not attributed to different quarry origins for the Tweed marbles. Neither Ammann 
& Whitney nor Mesick, Cohen, Waite went so far as to characterize the observed 
behavior as being indicative of Tuckahoe or Sheffield marble. While the puipose of their 
work was not to come to any conclusion on this point, their data leave the door open for 
further investigation. 

With the wealth of high technology now available for the analysis of building 
materials, more traditional analysis is often neglected. Along with some cursory optical 
microscopy, the most advanced analytical tools available at the time, SEM, XRD, and 
EDXA, were applied to marble specimens from the Tweed Courthouse. Suiprisingly, the 
characteristics of Tuckahoe and Sheffield marble have not been investigated extensively 



Previous Analysis and Cleaning Page 67 

using thin section microscopy. The only known thin section analysis of Tuckahoe marble 
was performed by Matero and Tagle (1995), and thin section has never been used with 
Sheffield marble. This method of investigation can yield a great deal of information about 
the composition and behavior of stone. For that reason, thin section microscopy was used 
in the laboratory research phase of this project to characterize the basic properties of the 
Tweed Courthouse marbles. The results of this investigation will be discussed in Chapter 
4. Thin section analysis may not entirely explain the differential weathering of marble 
observed at the Tweed Courthouse in the past, but it will help to characterize the 
microstructures of Tuckahoe and Sheffield marble. These parameters can offer insight 
into the weathering behavior of the stone as it has been documented in the more than 120 
years of the courthouse's existence. 



CHAPTER IV 
Analysis and Observations 

Rationale for Testing Program 

Marble has spawned a long history of investigation. Historians, archaeologists, 
geologists, engineers, and, more recently, fine arts and architectural conservators have all 
taken an interest in researching the structure, composition, and behavior of the "noblest" 
of building materials. As a result of this interest, there is no lack of published material on 
a number of topics related to marble, including its mechanisms of decay. 

One area of marble research has focused consistently on primary causes of decay. 
Geologists and engineers have prompted the larger part of the dialogue on this topic to 
date. At least since 1884, with the publishing of the Tenth Census and its report on 
building stones in the United States, observers have speculated on the mechanisms 
responsible for the initial deterioration of marble. '°" Alexis Julien believed that the 
crystalline structure of marble, in which grains are not held together by any kind of 
cement but rather by extreme tension, was susceptible to very slight variations in 
temperature. He surmised that heating and freezing cycles could cause the grains to slide 
past each other, wearing down the original intergranular cohesion on a microscopic level. 
Once this had been accomplished, the stone was vulnerable to other decay mechanisms. 
Julien placed the effects of temperature ahead of other factors in trying to explain the first 
stages of structural breakdown. 



" Julien's observations in "The durability of building stones in New York City and vicinity" are discussed in 
Chapter II. 

68 



Analysis and Observations Page 69 

In 1919, David Kessler, a researcher at the Bureau of Standards in Washington, 
D.C., observed that heating may cause permanent deformation in marble."^'' Once a 
marble sample had been exposed to repeated heating, its actual dimensions appeared to 
change inalterably. Widhalm, Tschegg, and Eppensteiner recount the history of research 
on the effects of thermal deformation of marble since that time.'°"* They write that 
Rosenholtz and Smith arrived at similar conclusions in 1949, as did Thomasen and Ewart 
in 1984, Monk in 1985, and Wilson in 1989. However, the general opinion among these 
scientists held the presence of moisture to be an important factor in determining thermal 
alteration. The permeability of thin marble slabs, and hence their capacity for water 
absorption, was thought to be a controlling variable in thermal deformation. 

Widhalm, et al. write that a secondary factor considered by Rosenholtz and Smith 
was the thermal anisotropic behavior of calcite. Dreyer in 1974 and Samen in 1991 also 
took this factor into account. Stiny in 1935, Neumann in 1964, and deQuervain in 1967 
concluded that thermal anisotropy of calcite grains was actually the most important 
determinant of the loosening of grain boundaries in marble after thermal cycling.' 

An explanation of the extreme thermal anisotropy of calcite is important in 
understanding the breakdown of marble. When heated, calcite does not expand 
uniformly in all directions. The linear coefficient of thermal expansion is a= (l/t)(dl/dt), 
where l=length, t= temperature, and the change in both is indicated by d. Materials 
like glass and cubic crystalline solids are isotropic. When a material has a lower 
crystallographic symmetry due to the preferred orientation or texture of the individual 



"*'' Kessler, D.W. "Physical and chemical tests on the commercial marbles of the United States," Technologic 

Papers of the Bureau of Standards. Government Printing Office: Washington, 1919. 

'*^ Widhalm, Clemens, Elmar Tschegg, amd Walter Eppensteiner. "Anisotropic thermal expansion causes 

deformation of marble claddings." Journal of Performance of Constructed Facilities, Feb. 1996, p. 5. 

'°' Ibid. p. 5. 

'°* Ibid., p. 7. 



Analysis and Observations Page 70 

grains, it may be anosotropic."^^ Widhalm et al. consider the direction of trigonal calcite 
monocrystals within a polycrystalline marble to be the chief determinant of deformation 
in marble slabs. The preferred orientation, or texture, of marble, as dictated by the 
layering of grains during the formation of sedimentary limestone and the processes of 
metamorphosis, in conjunction with the anisotropy of calcite, largely determines the early 
loosening of grain boundaries leading to decay. In calcite, anisotropy is expressed as a 
comparison of thermal expansion in two directions: parallel (all = +26.1 0"^K" ) and 
perpendicular (olL=-6.1 0^ K"') to an imaginary c-axis through the center of a crystal. 
"^^These demonstrate the directional difference in expansion and contraction when a 
calcite crystal is heated. 

Based on their experimental measurements, Widhalm et al. concluded that: 1) 
residual dilatation (permanent deformation) occurs after heating; 2) the first round of 
heating is the most important for dilatation; 3) the direction of expansion is dependent on 
the crystallographic preferred orientation (texture); and 4) water absorption capacity 
increases with the number of heating cycles. Thermal anisotropic expansion of calcite, 
therefore, is believed to the first step in the breakdown of calcitic marbles. Significantly, 
the temperature variations leading to a breakdown of cohesion along grain boundaries do 
not have to be great. Normal seasonal and day-night differences in temperature, even in 
temperate climates, are sufficient for this to occur. '°^ 

Like Julien, Siegesmund et al. concluded that the major effect of thermal 
dilatation is a reduction of cohesion along grain boundaries and the formation of inter as 



'°' Ibid., p. 7. 

'°* Widhalm etal., p. 35. 



"" Siegfried Siegesmund, Thomas Weiss, Axel Vollbrecht, and Klaus Ullemeyer. "Marble as a natural building 
material: rock fabrics, physical and mechanical properties." Zeitschrift der Deiitschen Geologischen 
Gesellschaft, Stuttgart, 1999, v. 150, p. 247. 



Analysis and Observations Page 71 

well as transgranular (intragranular) cracking. "° They expand on Widhalm's analysis by 
considering two-phase marbles that may be composed of calcite and its close cousin, 
dolomite. Dolomite has a high thermal coefficient a, meaning that it readily expands 
when heated. The experimental linear coefficient of thermal expansion in dolomite was 
reported as follows: a minimum equals11.9 X 10^K"', while a maximum equals13.8x 10'^ 
K"'.'" For calcite, a minimum is 2.4x10'^K"', and a maximum is 6.7 x 10'^K"', smaller 
than dolomite. Additionally, the degree of anisotropy in dolomite is small, meaning that 
it expands more or less equally in all directions. In contrast, calcite is highly anisotropic, 
as shown above."" Consequently, the calcite to dolomite ratio of a marble can affect 
property changes. Siegesmund et al. reported that the interdependence between the 
coefficient of thermal expansion and the calcite content per volume appeared to be 
linear." The more calcite present in a marble sample, the lower the overall observed 
thermal expansion. Likewise, the more dolomite, the greater the overall observed 
thermal expansion. However, one would expect anisotropic thermal expansion to be 
greater in marbles with a higher calcite content. 

Widhalm et al. consider texture, shape fabric, and microcracks to be the 
controlling variables of thermal dilatation, and these are additionally controlled by the 
mineralogical composition of the marble. They also found a correlation between grain 
size and the formation of microcracks. Marbles with a larger grain size exhibited 



"° Siegfried Siegesmund, Klaus Ullemeyer, Thomas Weiss, Elmar K. Tschegg. "Physical weathering of 
marbles caused by anisotropic thermal expansion." International Journal of Earth Sciences, 2000, v. 89, p. 
177. A 1986 article by Reeder and Markgraf provides a thorough discussion of the opposite thermal expansion 
behaviors of calcite and dolomite. See Richard J. Reeder and Steven A. Markgraf, "High temperature crystal 
chemistry of dolomite," American Mineralogist, 1986, v. 71, pp. 795-804. 
'" Ibid., p. 178. 
"-Ibid., p. 178. 
'"ibid., p. 178. 



Analysis and Observations Page 72 

cracking at significantly lower temperatures than fine-grained marbles. Conversely, 
only the finer-grained marbles seemed to undergo plastic, thermally-induced bowing. 

An additional parameter of thermal deformation of marble considered by 
Siegesmund et al. was grain boundary geometry as determined by recrystallization 
processes. In their analysis, fracture strength appeared to correlate with grain boundary 
geometry. Straight or slightly curved grain boundaries were characterized as showing 
weakening phenomena at lower tensile, compressive, or shear stresses than grains with 
interlocking or strongly curved grain boundaries."^ Thomas Weiss et al. also found that 
straight grain boundaries were less resistant to crack propagation than interlocking or 
curved grain boundaries."^ Tschegg et al. (1999) saw a correlation between the ability to 
withstand thermal deformation and the observable properties of grain orientation and 
grain size. "^ In their experiments, finer-grained marbles with a low degree of grain- 
orientation, like Carrara marble, were more susceptible to thermal deformation than 
larger grained-marbles with a more distinct orientation, such as the Hartensteiner marble. 

Clearly, much of the most interesting research into the primary causes of marble 
decay has focused on thermal anisotropy of constituent minerals and the related 
breakdown of cohesion along grain boundaries. The quantification of rock fabrics has 
shown to be very useful in understanding the weathering of marbles, and it is an approach 
that is worth taking in a study of marble from the Tweed Courthouse. Microstructure is 
as important to the processes of weathering as mineralogical composition. 



"^ Ibid., p. 180. 

"'Ibid., pp. 180-181. 

' '* Thomas Weiss, Bernd Leiss, Heidrun Opperman, and Siegfried Siegesmund. "Microfabric of fresh and 

weathered marbles: implications and consequences for the reconstruction of the Marmorpalais, Potsdam." 

Zeitsclirift der Deiitsclien Geologischen Gesellschaft, Stuttgart, 1999, v. 150, p. 329. 

"^ Elmar K. Tschegg, Clemens Widhalm, and Walter Eppensteiner. "Ursachen mangelnder Formbestiindigkeit 

von Marmorplatten." Zeitsclirift der Deiitscheii Geologischen Gesellschaft, Stuttgart, 1999, v. 150, pp. 283-297. 



Analysis and Observations Page 73 

The current body of research suggests the following parameters for investigation: 

1 ) Characterization of constituent and accessory minerals and their interaction 

2) Characterization of the microcrack population, especially inter and intragranular 
cracking 

3) Analysis of preferred orientation and its relation to thermal deformation 

4) Analysis of grain dimensions and grain size distribution 

5) Analysis of grain boundary geometry 

6) Observations about mechanisms of decay 

Testing Program 

As discussed in Chapter III, microscopic thin section analysis is a powerful tool 
for the characterization of basic stone properties. Surprisingly, this method has never 
been used at the Tweed Courthouse. Because of the amount of information it can 
provide, microscopic thin section was chosen as the primary method of analysis for the 
investigation of Tuckahoe, Sheffield, and Cherokee marbles used in the construction and 
restoration of the Tweed Courthouse exterior. By observing a sample of stone sliced to a 
thickness of 1 micron, some of the most important questions about the weathering 
behavior of a stone can be answered. This is especially true when correlated with 
patterns of field-observed weathering phenomena. Features that can be differentiated and 
quantified are: the general mineralogical composition and the ratio of different minerals 
to one another; grain size, shape, distribution, perimeter, and boundary; microcrack 
population; and the existence of surface pollutants or biological growth. 

As part of the process of creating thin section slides, each sample was vacuum- 
impregnated with blue dye to highlight the microcrack population, and half of each slide 



Analysis and Observations Page 74 

was stained to indicate the presence or absence of calcite, the dominant mineralogical 
constituent of most marble. What remained of the original sample was retained for 
comparison with the thin section slide. 

The original samples were also analyzed to understand the differences in 
fracturing between fresh and weathered marble. Grimm observed a relationship between 
the degree of weathering and the amount of intracrystalline cracking in marbles. Fresh 
marbles tended to have subvalent to prevalent granular cohesion (20%- 100% 
intragranular fracturing), while weathered marbles tended to have subvalent granular 
cohesion (0%-70% intragranular fracturing). He concluded that weathered marble 
usually has a higher degree of intergranular cracking than fresh marble because of loss of 
cohesion along grain boundaries."^ More weather-resistant marbles were characterized 
by a higher degree of intragranular cracking. Observed differences in granular cohesion 
between weathered and unweathered marble can be an indicator of the material's 
resistance to weathering. 

Augmenting a visual analysis of the thin section slides, computer-aided analysis 
of the slides using Bioquant software was performed. Bioquant is a Windows-based 
application designed to perform quantitative analysis on organic matter such as cell tissue 
for biological and pharmaceutical research. It has not been used widely for building 
materials research. This software was selected by the Architectural Conservation 
Laboratory at the University of Pennsylvania for microstructural analysis of porous 
building materials at Mesa Verde National Park as part of a research grant from the 
National Park Service. By applying Bioquant to marble in thin section, it was hoped 



"* Wolf-Dieter Grimm, "Beobachtungen und iiberlegungen zur Verformung von marmorobjekten durch 

gefugean{\ockemng." Zeitschrift der Deutschen Geologischen Gesellschaft, Stuttgart, 1999, v. 150, pp. 199- 

201. 

"^ Grimm, p. 202. 



Analysis and Observations Page 75 

that some of the analysis traditionally performed by the researcher, such as calculation of 
individual grain size, shape factor, and perimeter, could be performed by the computer. 
The first step of this process involved making images of the thin section slides readable 
by the software. Photomicrographs of each slide were scanned into the computer, and the 
photos were imported into Adobe Photoshop . The grain boundary geometries in a 1 
square cm area of the slide were then "hand drawn" in Photoshop . After this, the 1 cm 
square images were opened in Bioquant , and four parameters for analysis were set: gram 
area, average diameter in a grain, perimeter, and Paris factor. Applying these parameters 
to the images provided data almost instantaneously. The data were then copied to Excel 
to calculate grain size distribution, gradation coefficient, and inequality grade. 

Paris factor, also known as shape factor, defines the irregularity of the grain 
boundaries. According to Weiss et al., it is equivalent to the ratio between circumference 
and a convex envelope of a grain: "for regular, smooth grain boundaries the Paris factor 
approximates the value of 1. The more the grain boundaries are irregular, the lower the 
Paris factor."'"^ The equation for Paris factor, calculated in Excel rather than 
Bioquant , is 4n (F/U'), where F=surface and U=perimeter. Including two additional 
parameters discussed by Grimm (1999), gradation coefficient (So=Vd75/d25) and 
inequality grade (U=d60/dl0) were calculated where d is the diameter of a specified 
percentage of the grains in a sample.'"' In general, the higher the "toothing factor" of 
interlocking grain boundaries, and the more irregular the grain boundaries, the stronger 
the grains cohere to one another. This can be an indicator of resistance to mechanical 
decay. 



'-"Weissetal., p. 317. 
'-' Grimm, pp. 199-201. 



Analysis and Observations Page 76 

Like Paris factor, gradation coefficient and inequality grade relate to the degree of 
mechanical resistance in a stone sample. Marbles with smaller grains tend to fracture 
more easily than those with larger grains. 

As a complementary approach to the thin section and Bioquant analyses, 
Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X- 
Ray Diffraction (XRD) were also applied to samples of the two stones. The information 
gained by cross-referencing scanning electron micrographs, elemental data from EDS, 
and mineralogical data from XRD with information from thin section analysis and 
Bioquant was useful in confirming the final conclusions. 

Gathering and Selection of Samples for Analysis 

Samples that were processed for thin section slides were gathered from a handful 
of sources. Most of the stone was collected on site. During the course of replacement, 
the most severely weathered exterior stone was removed and discarded. Drilling cores, 
abacuses on the capitals, dumpsters on the scaffolding, and an assortment of other 
locations accounted for most of these specimens. Therefore, a general location of each 
sample piece is known, but the exact origin of each piece from a location on the building 
is not usually known. Understandably, it is not possible to know the original position of 
the stone in the quarry from which it was removed, either. This information, especially 
any details about layering and each sample's relation to other strata in the quarry, would 
be helpful for the kind of petrographic analysis that is being done as part of this research. 
Some of this information can be inferred from the visible signs of layering in the samples, 
but it has not been included in the current analysis. 



Analysis and Observations Page 77 

Other stone, especially the replacement Georgia Cherokee, was taken from new 
blocks delivered to the site. Some pieces of the stone were detached during handling or 
were removed during the setting of the new cornice, which is composed entirely of the 
Cherokee marble. Some stone was also taken from blocks of salvaged stone from the 
building itself. The decayed cornice provided much of the dutchman material for the 
lower, more visible areas of the building. 

A few samples of stone also derive from the actual Briggs quarry in Sheffield, 
Massachusetts. Large blocks have remained on the quarry site since the last century and 
these were purchased, shipped, finished, and dressed for use as replacement stone. 
Consequently, the weathering of the Sheffield marble, particularly in the lower, more 
visible areas of the building where it is being used again, will be a significant factor in the 
future behavior of the exterior stone. 

A matrix of the samples collected is provided in the Appendix 2. Each piece has 
been assigned a number and any relevant information about it has been included. Some 
samples have had thin section slides made from them, but most have not. The general 
location of each sample on the building has been provided in the matrix. General calcite 
content is given, and each sample has been labeled weathered or fresh. It is also noted if 
SEM or XRD has been performed, and if a thin section slide has been made from the 
sample. 

The selection of thin section slides for comparison was based on a positive 
identification of each as deriving from either the Tuckahoe area of Westchester County, 
New York or the Sheffield quarry in Massachusetts. It was essential that the 
identification of each be accurate. This main criterion narrowed the number of useable 
thin section slides considerably. The slides themselves have been numbered based on the 



Analysis and Observations Page 78 

matrix identification number plus a single-letter prefix, "T", "S", or "G" to denote the 
likely origin as either Tuckahoe, Sheffield or Georgia Cherokee. 

Tuckahoe samples derive from locations on the building that historically have 
been characterized as being built of Tuckahoe marble. The Eidlitz wing and the North 
Portico of the Kellum section of the building were the primary sources of Tuckahoe 
marble for these purposes. Another important criterion was visual similarity between 
samples of Tuckahoe taken from these areas. Sample number 8, labeled T-8 in thin 
section, is part of a drilling core taken from the cornice. Its textural and mineralogical 
properties are a close match for samples taken from the areas of the building known to 
have been built with Tuckahoe marble. T-8 was the best approximation for a recently 
quarried sample, since the Tuckahoe quarries have not been open since the early decades 
of the 20"' Century. 

Likewise, Sheffield samples were taken only from areas known to have been built 
with a mixture of Sheffield and Tuckahoe. Samples of stone from the Briggs quarry, one 
of which is numbered 15 in the matrix and S-15 in thin section, were used to match 
samples from the building for comparison. One block of stone from the building, 38 in 
the matrix and S-38 in thin section, is analyzed as fresh Sheffield, because it was large 
enough that an area with no decay could be obtained several centimeters beneath the 
surface. S-36 and S-37 are exact textural and mineralogical matches for the S-15 sample 
from Sheffield and are treated as weathered samples of the stone. 

All Georgia Cherokee samples derive from blocks of the stone shipped to the site. 
Their identity was easier to ascertain than that of the other two types of stone. 

The final selection of samples used in this analysis will provide more uniformity 
within a marble type grouping than may actually exist on the building. The observations 



Analysis and Observations 



Page 79 



are not intended to characterize the materials on the building per se. Rather, they are 
intended to broadly characterize some of the qualities of fresh and weathered marble 
from the Tuckahoe quarries in New York and the Sheffield quarry in Massachusetts. 

Characterization of Samples 



n M I M I I 

cm 1 



Figure 4.1: A fresh Tuckahoe surface from sample Number 8. 



Fresh Tuckahoe 

Thin section analysis of fresh Tuckahoe marble was limited to slide T-8, which 
was taken from sample 8, a drilling core found at the cornice on the south end of the east 
facade. The core was drilled to make room for a large anchor installed to secure the new 
cornice stones. Figure 4. 1 shows a typical cut surface of the sample. 

Mineralogical Characterization: A cursory visual inspection of sample 8 shows 
that the fresh Tuckahoe marble is a very white, medium-grained stone with some light 



Analysis and Observations Page 80 

brown inclusions. Staining on the T-8 thin section slide produced a pale rose color, 
indicating that the dominant mineralogical constituent is probably dolomite. Upon closer 
inspection, many small flecks of calcite, stained a darker red color, are scattered 
throughout the sample (see Figures 4.2 and 4.3.) This pattern is repeated in all of the 
weathered Tuckahoe samples from the Kellum and Eidlitz sections of the building. 
Calcite and dolomite are difficult to differentiate in the absence of staining or laboratory 
testing, and the combination of the two in such a uniform mixture was not expected based 
on previous analysis. This combination may affect some of the properties seen in the 
weathered samples. 

In addition to the primary component dolomite and the secondary component 
calcite, numerous other accessory components were evident in thin section. The presence 
of phlogopite and tremolite was noted, as was the presence of a number of other minerals 
that could not be easily identified. On a microscopic level, the fresh Tuckahoe is very 
heterogeneous for a stone that appears to be uniform. Figures 4.2, and 4.5 show typical 
views in thin section. 

Structural Characterization: The structure of the fresh Tuckahoe sample is not 
uniform, and the grain fabric is irregular. Some areas are highly crystalline with 
interlocking grain boundaries, composed mostly of dolomite and calcite, while others are 
characterized by a random mixture of minerals and grain sizes and varied grain boundary 
shapes. The grain boundaries in the uniform areas are angular but not interlocking. 
Boundary interfaces are generally linear. Figures 4.2 and 4.4 show the compact structure 
of the sample with characteristic pockets of mixed inclusions. 

The grains also have a distinct degree of preferred orientation. This is common in 
Tuckahoe marble, which often contains layers along which the stone will tend to break. 



Analysis and Observations Page 81 

Sample T-8 was cut to demonstrate this type of layering. Figure 4.4 shows the transition 
between a layer of mixed minerals and a more purely uniform layer of dolomite, calcite, 
and a few inclusions. 

Microcracking: The fresh sample had very little microcracking. Vacuum 
impregnation of the thin section sample with blue dye did not reveal significant loss of 
cohesion along grain boundaries or fracturing across grains. Figure 4.6 shows the surface 
of the fresh stone in the upper portion of the photo and no visible fractures. The surface 
of the core seems relatively impervious to moisture penetration. 

Surface Fracturing: An idea of grain cohesion can be gathered by comparing the 
amount of inter and intragranular cracking in different stones. For this investigation, 
surface fracturing was investigated by looking at a fractured surface under a 
stereomicroscope (Figure 4.7). In the fractured surface of sample 8, intragranular 
cracking, obvious by the jagged cleavage across the stone, predominated. Intragranular 
cracks accounted for about 70% of the cracking, and intergranular cracks accounted for 
about 30 %. These percentages were cross-referenced by counting the number of inter 
versus intragranular cracks in 50 grains on the thin section slide. The slide analysis 
yielded a similar breakdown of 60% intragranular to 40% intergranular cracks. The 
percentage of intragranular cracks observed, around 60%, would place it in the category 
of prevalent to equivalent granular cohesion according to Grimm (1999). 

Bioquant Analysis: Analysis of the fresh Tuckahoe thin section slide using 
Bioquant showed that 1 square cm contained 207 individual grains. The digitized image 
of grain boundary outlines in 1 square cm of sample 8 is seen in Figure 4.8. The average 
grain perimeter was 2.35 mm, the average grain diameter was 0.52 mm, and the average 
grain area was 407, 500 square microns. The Paris factor was calculated to be 0.53 in 



Analysis and Observations Page 82 

comparison to a perfect convex grain envelope of 1 . Additional calculations made with 
the data obtained from Bioquant® showed that 62% of the grains were between 300 and 
1 180 microns in diameter. The distribution was even between 150-300, 300-600, and 
600-1800 microns in diameter. 26% were smaller than this, while 12% were larger. The 
gradation coefficient was calculated to be 2.28 and the inequality grade was calculated to 
be 5.1. 

An individual summary of results for T-8 is provided in Table 4.1. A summary of 
all Bioquant® data and related results for tested samples is given in Appendix 3. 

Decay Mechanisms: Although T-8 shows no traces of decay, it has some 
characteristics worth noting for discussion of the weathered samples. Foremost among 
these is the heterogeneous mixture of minerals already discussed. Phlogopite, tremolite, 
and iron minerals, among others, have been observed in the past in Tuckahoe marble and 
these are in abundance in thin section slide T-8. Calcite, visibly indistinct from dolomite 
without staining, could also be a factor in the decay of fresh Tuckahoe marble. The 
different properties of these minerals, including coefficients of thermal expansion and 
water absorption capacities, contribute to create a relatively unstable marble. 

Tuckahoe's acceptable but not outstanding performance as an exterior cladding 
could derive from the interaction of texture and mineralogical composition. Tschegg et 
al. (1999) characterized large-grained marbles with strong preferred grain orientation as 
more resistant to thermal deformation than fine-grained marbles with weak grain 
orientation. Fresh Tuckahoe marble has larger than average grain size and a distinct 
preferred orientation. This is offset by the presence of micaceous inclusions that 
compromise cohesion along the grain boundaries. A marble without the diverse 
behavior of these inclusions may perform better. Conversely, a marble without as many 



Analysis and Observations 



Page 83 



inclusions but also without a distinctly preferred grain orientation may not perform as 
well as Tuckahoe marble. On the surface at least, the combination of various minerals 
would seem to facilitate decay (see Figure 4.4). 



T-, \ 



n * 



»~ "V T 1 



4-K 



, x. y 




""'Ui'-" 





J- 



.i*!r- 








^^ 

:.i . . __ "^ _.^^ -1 ^ ./.«^ ,^c^»t^v . 

Figure 4.2: A typical view of fresh Tuckalioe marble from tiiin section slide T-8. Red stained calcite 
is interspersed with dolomite. The structure appears uniform and crystalline at the top of the 
photomicrograph. In the lower left, the structure appears more conglomerated. 5x magnification, 
cross-polarized light. 





Analysis and Observations 



Page 84 







Figure 4.3: Calcite and dolomite distinguislied by calcite staining. Lamellar twinning can be seen in 
crystals to the right of the photomicrograph. The structure is very compact and uniform in some 
areas but less so in others. The grain boundary shows no separation between crystals. lOx 
magnification, cross-polarized light. 




Figure 4.4: Dolomite, red-stained calcite, and phlogopite at the surface of the fresh Tuckahoe sample 
on slide T-8. Different expansion behavior during thermal cycling will probably cause surface 
pitting.This image is an interesting contrast to Figure 4.19, a similar but weathered surface. 20x 
magnification, cross-polarized light. 



Analysis and Observations 



Page 85 







Figure 4.5: Numerous inclusions are seen in the lower half of the picture. The green inclusion 
appears to be tremolite. while the numerous oblong inclusions are phlogopite. The variety of 
minerals creates a heterogeneous structure. 5x magnification, cross-polarized light. 







Figure 4.6: An absence of microcracking is evident in this photomicrograph of slide T-8. Vacuum 
impregnation with blue dye did not reveal any fractures. The clean surface is seen in the upper 
portion of the photomicrograph bordered by the blue dye. Close-up of 5x magnification, cross- 
polarized light. 



Analysis and Observations 



Page 86 




Figure 4.7: A fractured Tuckahoe surface from sample 8 seen in raking light. Intragranular 
cracking is more common than intergranuiar cracking. 7.5x magnification, fiber-optic illumination. 




Figure 4.8: Digitized grain boundary image of 1 square cm of Tuckahoe slide T-8. 



Analysis and Observations 



Page 87 



BIOQUANT ANALYSIS: SUMMARY OF DATA 



T-8 Fresh Tuckahoe Marble 


Average Grain Area (square microns) 


407,500 


Average Grain Diameter in Sample (microns) 


522 


Average Grain Perimeter (microns) 


2,345 


Average Grain Paris Factor 


0.53 


Number of Grains in 1 Square cm 


207 


Gradation Coefficient (So=Vd75/d25) 


2.28 


Inequality Grade (U=d60/d10) 


5.iq 



GRAIN SIZE SUMMATION 



Sieve Number 


Size (microns) 


Number of Grains 


Percent 


200 


0-75 


15 


7.25% 


100 


75-150 


38 


18.36% 


50 


150-300 


43 


20.77% 


30 


300-600 


44 


21.26% 


16 


600-1180 


42 


20.29% 


8 


1180-2360 


24 


1 1 .59% 




>2360 


1 


0.48% 



Percent of 
Grains 



T-8 Grain Size Summation 



25% / 




20% '^ 


r 








15% '' 




-— 


10% ' 


/ 


— 


5% 


/ "~ 


— 


0% 


A m. 


._. 



in 



o 
in 



(D ^ 




Grain Size (microns) 



Table 4.1 Summary of Bioquant data and related measurements for slide T-8. 



Analysis and Observations 



Pa ge 88 







--A 



Figure 4.9: Sample 1, a typical weathered Tuckahoe surface. Individual grains have been exposed 
and rounded. The original white color has turned to a yellowish brown. 



Weathered Tuckahoe 

Thin sections of several stone samples were classified with relative certainty as 
weathered Tuckahoe marble. Those that will be referred to in this section were taken 
from the North Portico of the Kellum section of the building and the Eidlitz section of the 
building, both of which are believed to have been built of Tuckahoe marble. A typical 
sample of weathered Tuckahoe is seen in figure 4.9. This sample was taken from an 
abacus on a capital in the North Portico. The exposed grains are rounded and the surface 
has turned to a yellowish brown color. 



Analysis and Observations Page 89 

Mineralogical Characterization: The thin section samples analyzed are identical 
to the fresh sample in mineralogical composition. Figures 4.10 and 4.1 1 show a piece of 
finer-grained Tuckahoe from the Eidlitz wing. Figure 4.12 shows another sample from 
the North Portico. They are predominantly made up of dolomite with uniformly 
distributed calcite grains together with phlogopite and tremolite. As shown in sample 1, 
in Figure 4.13, pyrite was seen in addition to other minerals. Slide T-IB was analyzed 
using Bioquant®. It also contains calcite along with the predominant dolomite and 
phlogopite inclusions. 

Structural Characterization: The structure of the observed weathered Tuckahoe 
samples is identical to that of the fresh samples. Like the fresh sample, the occasionally 
composite nature of the weathered samples often conveyed little uniform structure. 
However, there was greater variation in grain size and grain boundary geometry. Some 
of the samples were characterized by straight but moderately angular grain boundary 
geometry, while others have an amoebic grain boundary. In most samples, the dominant 
grain size was in the medium range, but within and across samples, there was a high 
degree of variation. In slide T-4, the grain size was smaller than any other Tuckahoe 
sample and the grains were considerably rounder (see Figure 4.10). On slide T-IB, seen 
in Figure 4.12, the grain size is more like the fresh Tuckahoe sample. Some of the grains 
in all of the weathered samples were so small that they were impossible to observe. 

Preferred orientation of the grains was distinct in many of the samples. In slide T- 
12B, the grains are preferentially oriented vertically in the image, but in slide T-4 the 
grains show a looser horizontal orientation relative to the image. In general, the 
weathered Tuckahoe samples are characterized by some degree of preferred orientation, 
medium grain size, and straight but angular grain boundary geometry. 



Analysis and Observations Page 90 

Microcracking: The microcracking seen in the weathered Tuckahoe thin section 
slides is characterized by a large amount of opening between and within grains. Intra and 
intergranular cracking were observed in the fresh sample, and they seem to proliferate 
after weathering with intragranular cracking becoming notably more prevalent. The 
degree of intragranular cracking correlates to the strength of cohesion between grains. 
The more crystalline and angular the grain boundary, and the more tightly cohered the 
grains, the more likely it is that a fracture will break through the grain and not around it. 
This is also a function of grain size, as described by Widhalm et al. (1996). Larger 
grained marbles are less susceptible to intergranular cracking than finer grained marbles. 
Some areas of the slides are so intensely cracked that it is difficult to imagine how they 
originally appeared (Figure 4. 12). Intragranular cracking is evident to a high degree in T- 
lA, a larger-grained sample, as shown in Figure 4.15. This behavior was seen in most of 
the weathered Tuckahoe samples except for the finer-grained T-4, seen in Figure 4. 10, 
which showed almost exclusive intergranular cracking. The prevalence of intragranular 
cracking in the larger-grained samples and the prevalence of intergranular cracking in the 
finer-grained samples confirms observations made by Widhalm et al. 

Surface Fracturing: By analyzing the fractured surface of sample 1 under the 
stereoscope, it was observed that roughly 40% of the cracking was intragranular, 
indicating subvalent to equivalent cohesion. The analyzed surface is seen in Figure 4.22. 
However, this did not appear to be the case deeper into the stone where the stone was not 
as weathered. A count of inter and intragranular cracking of 50 grains at a greater depth 
on thin section slide T-IA produced a breakdown of roughly 30% intergranular to 70% 
intragranular cracking, indicating prevalent to equivalent grain cohesion. As expected, 
intragranular cracking predominated in the deeper areas of the weathered Tuckahoe, 



Analysis and Observations Page 91 

which were slightly less weathered. The percentage of intragranular cracks observed 
overall, around 40%-50%, would place it in the category of equivalent granular cohesion 
according to Grimm (1999). On the building itself, the areas of weathered Tuckahoe 
marble are degraded enough that they can be broken off with a minimum of force. Loose 
individual grains can be scraped from the surface like sand. 

Bioquant® Analysis: As was done with the fresh sample, grain boundaries in 1 
square cm of thin section slide T-IB were drawn and digitized in order to calculate a set 

(R) 

of parameters in Bioquant . The digitized image of grain boundary outlines in 1 square 
cm of sample 1 is presented in Figure 4.23. 145 individual grains were calculated in 1 
square cm. The average grain perimeter was 3.04 mm, the average grain diameter was 
0.59 mm, and the average grain surface area was 590,318 square microns. The Paris 
factor was calculated to be 0.46 in comparison to a perfect convex grain envelope of 1 , 
the lowest of the marbles. Additional calculations made with the data obtained from 
Bioquant showed that 56% of the grains were between 600 and 2,360 microns or greater 
in diameter. However, 44% of the grains were smaller than 600 microns. The largest 
single diameter category was 600 microns, which accounted for 23% of the whole. 18% 
of the grains were 75 microns wide or smaller. The gradation coefficient was calculated 
to be 2.76 and the inequality grade was calculated to be 10.70. 

These measurements are close to the measurements made for T-8, the fresh 
sample. Average grain area, however, was nearly twice as large as the fresh sample and 
the Paris factor was significantly lower, reflecting the unusual grain boundary geometry, 
which may be the result of recrystallization. Grain size distribution was not as even as in 
the fresh sample. An individual summary of results for T-IB is provided in Table 4.2, 



Analysis and Observations Page 92 

and a summary of all Bioquant data and related results for tested samples is given in 
Appendix 3. 

Decay Mechanisms: Several factors were observed to have some bearing on the 
extreme, intragranular microcracking of the weathered Tuckahoe samples, h-on content, 
surface gypsum formation and recrystallization, as well as the behavior of accessory 
minerals were considered to be important. 

Figure 4.16 shows etching, cracking, and iron staining on the surface grains of T- 
IB. Particularly near the exposed weathered surfaces, iron staining was more 
pronounced. The source of the iron staining could not be traced to any specific inclusions 
in the marble. Rather, the iron seemed to originate from the dolomite crystals themselves 
(see Figure 4. 17). This may be explained by the chemical makeup of the Tuckahoe 
sample, which was analyzed using XRD and will be discussed at the end of the chapter. 
The characteristic jagged etching pattern of weathered dolomite was observed on the 
exposed edge of sample T-IB. When observed under high magnification, the upper 
portions of the weathered surface grains seemed to have taken on a sponge-like structure 
due to gypsum formation. 

This salt was also observed to have crystallized in the pores created by the 
microcracks, further accelerating cracking below the surface of the stone. This occurs 
when airborne pollutants land on the stone surface and convert calcium to gypsum in the 
presence of moisture. Figure 4.18 shows a typical layering of pollutant deposition on a 
Tuckahoe surface. After repeated absorption of water into the substrate, gypsum 
crystallizes within the pores of the weathered marble, as seen in Figure 4. 19 and 4.2 1 . In 
the same photomicrograph, iron spots are also seen on individual dolomite crystals. The 
same is seen in Figures 4.20 and 4.21closer to the weathered surface. Microcracks 



Analysis and Observations Page 93 

emanating from a calcite crystal wedged between two dolomite crystals harbor 
recrystallized salts. 

The opposite thermal dilatation behavior of calcite and dolomite is one possible 
reason for microcracking at this location and elsewhere in the Tuckahoe marble. While 
dolomite is quicker to expand, its anisotropy is low. As Siegesmund et al. (1999) noted, 
in a pure dolomitic marble, the thermal expansion coefficient is large while the degree of 
anisotropy is small. Calcite, on the other hand, is slower to expand but is highly 
anisotropic. This may explain why some microcrack networks in the weathered 
Tuckahoe samples seem to be connected by nodes of calcite. A random but distinct 
distribution of calcite crystals within the largely dolomitic marble could contribute to 
early microcracking. 

The action of mineral inclusions within the stone is a major source of surface 
decay. As explained by Lewin and Charola, platy or fibrous inclusions occurring at or 
just below the surface trap liquid water.'"" Immense interlaminar pressure is built up in 
the micaceous phlogopite by the absorption of water during freeze thaw cycling. This 
pressure causes the inclusion to expand and eject any surface material above it. In this 
way, inclusions within 1-3 millimeters of the surface are capable of swelling and bursting 
in this way. Phlogopite and tremolite were evident in all of the Tuckahoe samples, and 
they are noted in Figures 4.13, 4.14, and 4.23. Their presence in this and other samples is 
undoubtedly responsible for some of the initial surface decay of Tuckahoe marble. 



'"" Seymour Lewin and A. Elena Charola, "Stone decay due to foreign inclusions." The Consen'ation of Stone 
II: Preprints of the Contributions to the International Symposium. Bologna, 27-30 October 1981, Part A: 
Deterioration. Bologna, 1981, p. 2 10. 



Analysis and Observations 



P age 94 




^#^-. :^<^.;-^' ^{^-^^ , 




•^"^ 



•V, 




^:^ ^- 



j>r- - ^ 



i 



Figure 4.10: Thin section slide T-4 from the Eidlitz wing. Calcite is interspersed with dolomite. The 
grains are much flner and rounder, and fewer inclusions are seen in this sample than in the fresh 
sample. Grains are oriented more or less horizontally. Intergranular cracking is indicated by the 
vacuum impregnated blue dye. 1.25x magnification, plane polarized light. 




















Figure 4.11: Thin section slide T-12B from the Eidlitz Wing. Again, calcite is interspersed with 
dolomite. Grains show a more or less vertical orientation relative to the photomicrograph. 1.25x 
magnification, cross-polarized light. 



Analysis and Observations 



Page 95 



-•^,^>-\--. ■' 
















;yf 



?v^ 



rr^-?''' 



>V 



V«.1 



-"^•; 



VUk 



:«•. 



>w^ 






r^; 



Figure 4.12: Thin section slide T-IB. Red-stained calcite is scattered tlirougliout, and oblong 
phlogopite inclusions are visible in the lower right. Cracking, seen in blue, seems to emanate from 
and connect the calcite grains. 5x magnification, plane-polarized light. 




Figure 4.13: Pyrite (left) and phlogopite (right) in a fractured surface of sample 1 seen under a 
stereomicroscope. 38x magnification, fiber-optic illumination. 



Analysis and Observations 



Page 96 




Figure 4.14: Slide T-lA,a typical weathered specimen with extensive microcracking. Crack networks 
are highlighted by vacuum-impregnated blue dye. Oblong phlogopite inclusions are visible at the 
center of the image. The exposed weathered surface is at the bottom of the picture. Photomicrograph 
is 1 cm wide, slide is unstained for calcite. 1.25x magnification, plane-polarized light. 




Figure 4.15: Intragranular cracking below a weathered surface in thin section slide T-IB, taken from 
an abacus on the North Portico. The original grain boundary is shown in yellow, cracks are 
indicated by the presence of blue dye, and intragranular cracks are indicated by red arrows. 50x 
magnification, cross-polarized light. 



Analysis and Observations 



Page 97 




Figure 4.16: Heavy etching, cracking, and iron staining of surface grains, slide T-IB. The 
weathered surface is bordered by the blue dye matrix. 5x magnification, plane polarized light. 




Figure 4.17: Iron staining and acid etching of surface dolomite crystals on slide T-IB. The surface 
appears at the top of the slide. Reddish iron spots seem to originate in the dolomite crystals 
themselves. Weathering has created an almost sponge-like structure in the exposed grains 20x 
magnification, plane polarized light. 



Analysis and Observations 



Page 98 




Figure 4.18: Layers of sulfurous pollution have formed a crust 1mm thick on this surface, from slide 
T-17. A combination of thermal expansion and infiltration by soluble salts probably leads to the 
surface decay of Tuckahoe marble. The substrate is seen at the bottom and the blue dye matrix is 
seen at the top. 5x magnification, plane-polarized light. 




Figure 4.19: Gypsum recrystallization within microcracks, slide T-IB. Due to its relative higher 
solubility, it has penetrated the stone and recrystallized, creating additional pressure in the openings. 
Iron spots are also visible. The rhombohedral structure of the dolomite grains is seen in the 
translucent cross-hatching patterns. 40x magnification, plane-polarized light. 



Analysis and Observations 



P age 99 




Figure 4.20: A surface grain of calcite wedged between two surface grains of dolomite, slide T-IB. 
The etching of dolomite beneath the calcite grain has created a saw-toothed pattern. Recrystallized 
salts are also seen. Thermal dilatation is the most probable cause of the microcracking surrounding 
the calcite grains. The space above the calcite grain may have held an ejected dolomite grain. 20x 
magnification, plane-polarized light. 




Figure 4.21: Recrystallization of calcite or salts in microcracks, slide T-IB. A red stained calcite 
grain is seen in the center of the photo surrounded on either side by white dolomite grains. Gypsum 
appears in a dolomite crack to the bottom right. 40x magnification, plane-polarized light. 



Analysis and Observations 



Page 100 




Figure 4.22: A fractured surface of sample 1. Intergranular cracking is more common in the 
weathered sample than in the fresh sample. Brown flecks of phlogopite are visible in the cracks. 7.5x 
magnification, fiber-optic illumination. 




Figure 4.23: Digitized grain boundary image of 1 square cm of Tuckahoe s!ideT-lB. 



Analysis and Observations 



Page 101 



BIOQUANT ANALYSIS: SUMMARY OF DATA 



T-1 B Weathered Tuckahoe Marble 


Average Grain Area (square microns) 


590,318 


Average Grain Diameter in Sample (microns) 


586 


Average Grain Perimeter (microns) 


3,046 


Average Grain Paris Factor 


0.46 


Number of Grains in 1 Square cm 


145 


Gradation Coefficient (So^^d75/d25) 


2.76 


Inequality Grade (U=d60/d10) 


10.90 



GRAIN SIZE SUMMATION 



Sieve Number 


Size (microns) 


Number of Grains 


Percent 


200 


0-75 


26 


17.93% 


100 


75-150 


22 


15.17% 


50 


150-300 


18 


12.41% 


30 


300-600 


33 


22.76% 


16 


600-1180 


25 


17.24% 


8 


1180-2360 


19 


13.10% 




>2360 


4 


2.76% 



Percent of 
Grains 



T-1B Grain Size Summation 



25%-, 



20% 



15% 



10% 



5% 



m 




''5 150 300 



600 1180 2360 >2360 
Grain Size (microns) 



Table 4.2: Summary of Bioquant data and related measurements for slide T-IB. 



Analysis and Observations 



Page 102 




Figure 4.24: A fresh Sheffield surface from sample 38. The sample is characterized by fine- 
grained "filler" grains between the larger grains. 



Fresh Sheffield 

The block of fresh Sheffield marble in Figure 4.24 is very white and comparable 
in color to the fresh Tuckahoe sample in Figure 4. 1. As discussed in the section 
"Gathering and Selection of Samples for Analysis," identification of Sheffield marble 
was made by a visual comparison of a block of stone from the defunct Sheffield quarry to 
samples from the building. This produced several very close matches for the weathered 
stone and one very close match for the fresh stone. The fresh Sheffield samples used for 
this analysis were gathered from the Kellum section of the building and the quarry. Thin 
sections slides were then made from these. 



Analysis and Observations Page 103 

Mineralogical Characterization: One of the interesting findings of this research 
relates to the composition of the Sheffield marble. In the range of samples picked as 
close matches with the quarry sample, there was strong uniformity of composition. 
Unlike the dolomitic Tuckahoe samples, all of the Sheffield thin section slides stained 
highly red for the presence of calcite. This suggests that the calcitic marble samples 
analyzed in previous rounds of testing derive from the Sheffield quarry. The most 
prominent inclusions seen in the fresh Sheffield samples were round silica grains. Silica 
was interspersed regularly throughout all of the Sheffield samples and generally forms 
along the grain boundaries. As a percentage of the total composition, silica was not great. 
Figure 4.25 shows a typical view with a regular distribution of silica. 

Structural Characterization: Comparing the samples in hand, without the help 
of a microscope, the structural differences between Tuckahoe and Sheffield marble are 
readily visible. The grain is noticeably finer in the Sheffield samples than in the 
Tuckahoe samples. A large amount of very fine, almost powdery grains seems to be 
mixed in with the larger but still fine grains, making the grain fabric somewhat irregular. 
At the visual level, the powdery material would not seem to be highly crystalline or to 
possess strong cohesion between grains. 

Sample 38 did not seem to exhibit a strong preferred orientation. Vague bands of 
layering approximately 0.5 cm thick were observed at the macroscopic level. Viewed 
under the polarized light microscope, thin section S-38 can be characterized as having a 
low preferred orientation. Some microcracks produced during the preparation of the thin 
section slide broke across the sample in a uniform direction, indicating that there was 
some preferred orientation of the grains (see Figure 4.26). Other samples were 
characterized by a noticeably irregular grain fabric. 



Analysis and Observations Page 104 

Crystallization of calcite seems to be the main determinant of grain shape. The 
calcite crystals have a roughly hexagonal outline. This was seen in the SEM images 
obtained from Sheffield samples. Consequently, the grain boundary geometry in the fresh 
Sheffield samples tends to be angular but straight. The grain-to-grain contacts tend to be 
smooth and not overly convoluted or crystallized, unlike those in slide T-IB. On the 
whole, the grain shapes of the fine-grainedTuckahoe and the fresh Sheffield were similar. 

Microcracking: Microcracks in the fresh Sheffield samples were more common 
than microcracks in the fresh Tuckahoe samples. This would seem to indicate a weaker 
overall structure. Even in the fresh sample slide, number S-38, microcracks were 
observed, probably as a result of thin section preparation (see Figure 4.26). One of the 
most distinct differences between Tuckahoe and Sheffield marble overall is the ratio of 
intergranular to intragranular cracking. Intergranular cracking was by far more common 
than intragranular cracking. According to Widhalm et al. (1996), the stone's medium to 
fine grain size may partially explains this. The lack of interlocking grain boundaries 
probably also contributes to this phenomenon. Smaller grains with low crystalline 
cohesion are more susceptible to cracking between grains and in general. Both of these 
factors are partially mitigated by the presence of a degree of preferred grain orientation, 
which directs fracturing along the bedding planes. 

Surface Fracturing: By analyzing a fractured surface of sample 38 under the 
stereoscope, it was observed that roughly 60% of the cracking was intergranular. The 
analyzed surface is seen in Figure 4.27. Analyzing 50 grains further below the surface of 
the thin section slide, the breakdown was closer to 80% intergranular cracks to 20% 
intragranular cracks. This was expected based on the observations about microcracking 
and structural characterization. The percentage of intergranular cracks was generally 



Analysis and Observations Page 105 

about 60%, very different from the fresh fractured Tuckahoe surface. The percentage of 
intragranular cracks observed, around 40%, would place it in the category of equivalent 
granular cohesion according to Grimm (1999). 

Bioquant Analysis: The grain boundaries in 1 square cm of thin section slide S- 
38 were hand-drawn and digitized in order to calculate the set of parameters previously 
discussed. 449 individual grains were calculated in 1 square cm, more than double the 
same number for the Tuckahoe samples. The digitized image of grain boundary outlines 
in 1 square cm of sample 1 is shown in Figure 4.28. The average grain perimeter was 
1.55 mm, a little more than half the size of the Tuckahoe samples. The average grain 
diameter was 0.36 mm, or 69% of the fresh Tuckahoe diameter. The average grain 
surface area was 41% of the Tuckahoe, or 168,726 square microns. The Paris factor was 
calculated to be 0.58, which is very close to that calculated for the fresh Tuckahoe. 
Additional calculations for grain size distribution made with the data obtained confirmed 
observations about the thin section. 82% of the grains were less than 600 microns in 
diameter. 52% of the grains were 300 microns in diameter or smaller. The largest 
category was 600 microns, which accounted for 30% of the number of grains counted. 
Only 2% of the grains were 2,360 microns wide or wider. The gradation coefficient was 
calculated to be 1.75, and the inequality grade was calculated to be 5.60. 

An individual summary of results for S-38 is provided in Table 4.3, and a 
summary of all Bioquant data and related results for tested samples is given in Appendix 
3. 

Decay Mechanisms: Slide S-38 is considered a fresh sample of Sheffield marble 
and therefore no decay was observed. Nevertheless, the existence of microcracking even 
in the fresh sample indicates a vulnerability to weathering phenomena. Figure 4.26 



Analysis and Observations 



P age 106 



shows clean intergranular cracking through the center of S-38. This fact will be useful in 
understanding decay in the weathered samples. 




Figure 4.25: Typical view of fresh Sheffield grains from slide S-38 in cross-polarized light. Calcite is 
seen throughout, and silica is seen distributed regularly in blue and orange. 1.25x magnification, 
unstained for calcite. 




Figure 4.26: Intragranular cracking seen on fresh slide S-38. Cracking appears to propagate parallel 
to the bedding plane in this case. 5x magnification, plane-polarized light, stained for calcite. 



Analysis and Observations 



Pa ge 107 




Figure 4.27: A typical fresh fractured Sheffield surface from sample 38. 7.5x magnification, fiber 
optic illumination. 




Figure 4.28: Digitized grain boundary image of 1 square cm of slide S-38. 



Analysis and Observations 



Page 108 



BIOQUANT ANALYSIS: SUMMARY OF DATA 
S-38 Fresh Sheffield Marble 



Average Grain Area (square microns) 



Average Grain Diameter in Sample (microns) 



Average Grain Perimeter (microns) 



Average Grain Paris Factor 



Number of Grains in 1 Square cm 



Gradation Coefficient (So=^d75/d25) 



Inequality Grade (U=d60/d10) 



J68726 
358 



1 ,548 
0.58 



449 



1.75 



5.60 



GRAIN SIZE SUMMATION 



Sieve Number 


Size (microns) 


Number of Grains 


Percent 


200 


0-75 


48 


10.69% 


100 


75-150 


81 


18.04% 


50 


150-300 


104 


23.16% 


30 


300-600 


135 


30.07% 


16 


600-1180 


71 


15.81% 


8 


1 1 80-2360 


10 


2.23% 




>2360 





0.00% 



S-38 Grain Size Summation 



35% 



30% 



25% 



Percent of 20% 
Grains 

15% 



10% 





300 600 1180 oQcn 

iiou 2360 J.2360 

Grain Size (microns) 



Table 4.3: Summary of Bioquant® data and related measurements for slide S-38. 



Analysis and Observations 



Page 109 



f 



"^WJV 





m 



Figure 4.29: A typical weathered Sheffield surface from sample 37. Exposed surface grains have 
been rounded. T he original white color has changed to a darker color than the weathered 
Tuckahoe. 



Weathered Sheffield 

Thin section slides for the weathered Sheffield marble were made from samples 
found on the Kellum section of the building. They were all medium to fine-grained, 
yellow to brownish in color, and demonstrated extreme friability. To a depth of up to 
several centimeters, individual grains could be scraped from the surface like sand. S-36 
and S-37 are taken from window surrounds at the west end of the south elevation. They 
closely resembled the quarried sample, S-15. S-15 is also considered because it presents 
different weathering phenomena, namely biological decay. A typical weathered surface 
rounded exposed grains is seen in Figure 4.29. 

Mineralogical Characterization: The weathered samples are mineralogically 
identical to the fresh sample, S-38. All weathered slides stained dark red for the 



Analysis and Observations Page 110 

presence of calcite. Like the fresh sample, silica grains were mixed regularly throughout. 
The silica grains were uniformly distributed along the grain boundaries and were often 
found in bands within the stone, as seen in Figure 4.32. Other mineral inclusions were not 
observed to exist in significant amounts. 

Structural Characterization: Again like the fresh sample, the structure of the 
weathered slides is characterized by a relatively fine grain size, low preferred orientation, 
and angular but straight grain boundaries, as seen in Figure 4.34. The very fine size of a 
large percentage of grains and the lack of strong cohesion between them contribute to a 
noticeably weak structure. Figures 4.30 and 4.3 1 show the characteristic structure of the 
weathered Sheffield. 

Microcracking: Intergranular microcracking was to be expected based on the 
previously described structural characteristics. Extreme microcracking was seen in all of 
the weathered samples. Intergranular cracking dominated while intragranular cracking 
was seen only to a small degree. Figures 4.3 1, 4.33, and 4.34 show the degree of 
cracking near the surface of a weathered Sheffield sample. 

Surface Fracturing: By analyzing a fractured surface of sample 37 under the 
stereoscope, it was observed that roughly 80% of the cracking was intergranular, more 
than the fresh surface. The analyzed surface is seen in Figure 4.35. Analyzing 50 grains 
further below the surface of the thin section slide, the breakdown was again about 80% 
intergranular cracking to 20% intragranular cracking. This was expected based on the 
observations about microcracking and structural characterization. The small gain size 
and lack of strong intergranular cohesion seem to determine the fracturing behavior in 
both weathered and fresh samples. The percentage of intragranular cracks observed. 



Analysis and Observations Page 111 

around 20%, would place it in the category of low granular cohesion according to Grimm 

(1999). 

Bioquant® Analysis: Slide S-15, taken from the quarry sample, was chosen to be 
analyzed in Bioquant®. Because its identity was certain, it provided a good control for 
the other samples taken from the building. The digitized image of grain boundary 
outlines in 1 square cm of sample 1 is seen in Figure 4.36. Much like the fresh sample, 
410 individual grains were calculated in 1 square cm. The average grain perimeter was 
1.47 mm, very close to the fresh sample. The average grain diameter was 0.35 mm. The 
average grain surface area was 191,383 square microns. The Paris factor was calculated 
to be 0.56. These measurements were very close to the measurements taken from the 
fresh sample. Additional calculations for diameter made with the data obtained were also 
close. 80% of the grains were 600 microns in diameter or less. 52% of the grains were 
300 microns in diameter or smaller. The largest category was between 300 and 600 
microns, which accounted for 28% of the number of grains counted. 4% of the grains 
were between 1,180 and 2,360 microns wide or wider. The gradation coefficient was 
calculated to be 1.91 and the inequality grade was calculated to be 4.70. 

An individual summary of results for S-15 is provided in Table 4.4. A summary 
of all Bioquant® data and related results for tested samples is given in Appendix 3. 

Decay Mechanisms: Several factors are considered to have some bearing on the 
extreme intergranular microcracking of the weathered Sheffield samples. The thermal 
anisotropy of calcite, a basic structural inability to resist thermal deformation, and the 
resulting capillary porosity are considered major mechanisms of Sheffield marble decay. 
The presence of silica inclusions is also considered to have some influence on the 
weathering of the marble. 



Analysis and Observations Page 112 

The thermal deformation of calcitic marble has been discussed earlier in this 
chapter. The behavior of heated calcite crystals in a polycrystalline matrix should be 
considered one of the primary factors affecting surface weathering. Preferred grain 
orientation within a polycrystalline matrix can also influence weathering properties. 
Tschegg et al. (1999) modeled the relationship between the grain configuration in a 
calcitic marble and the observed deformation or damage. In their analysis, increased 
random orientation correlated to increased damage due to thermal deformation. This may 
contribute to the pervasive structural disintegration of the weathered Sheffield with its 
random orientation of grains. Figure 4. 38 shows the orientation of grains in slide S-15, 
frequently at 45 'or 90' angles to each other. 

The initial loosening of the surface grains due to day/night thermal cycling makes 
the substrate more vulnerable to other mechanisms of decay. Figure 4.37 shows a 
surface calcite grain detaching from sample S-37. This type of surface opening permits 
infiltration of salts in solution, which will contribute to further structural breakdown. On 
the south side of the building, where samples 36 and 37 were located, the amount of daily 
sunlight exposure is higher than any other place on the building. The samples taken from 
this area have been exposed to daily thermal cycling for over 1 15 years. 

Surface deposition of sulphuric compounds in precipitation etches the surface 
grains and introduces secondary mechanisms of decay into the substrate. Figure 4.38 
gives some idea of a typical etched surface with numerous fine microcracks that facilitate 
capillary absorption of water. The extremely porous and stained state of these and other 
pieces of stone on the south facade is the chief reason for their current replacement. 
After the heated, exposed surface creates fine openings between grains, capillary 



Page 113 



Analysis and Observations . 

absoq)tion is powerful enough to bring sails deeper into the interior of the stone. The 
presence of silica and other inclusions also probably affects the formation of microcracks. 
Another type of decay was seen in the weathered sample taken from the Sheffield 
quarry. Figure 4.39 shows colonization of the surface by biological growth. Unlike the 
samples from the building, the quarry samples had little evidence of pollution. A fine, 
dark layer of fungus covered the surface instead. In thin section, acid breakdown of 
calcite by microbial communities has created rounded holes in the surface. A porous 
structure was seen to a depth of 2+ mm. The difference between this sample and the 
surface that have weathered in New York City points out the importance of regional, 
local and even micro-climate in the weathering of exterior stone. 




Figure 4.30: Calcite with occasional silica (white) along the grain boundaries on slide S-15. Note red 
staining for calcite. 5x magnification, plane-polarized light, stained for calcite. 



Analysis and Observations 



Page 114 




Figure 4.31: Even in the quarry sample S-15, intense microcracl<ing was seen. Notice tlie jumbled of 
grain sizes and the lack of preferred orientation. Cracks are indicated by the vacuum-impregnated 
blue dye. 5x magnification, plane-polarized light. 




Figure 4.32: Silica inclusions sometimes appear in bands. Here they are gathered in the center and 
bottom of the slide, S-36. 1.25x magnification, plane-polarized light, stained for calcite. 



Analysis and Observations 



P age 115 




Figure 4.33: Extreme surface friability on slide S-37. The surface is bordered by blue abo> e. Note 
the predominance of intergranular cracking and siliceous inclusions. 5x magnification, plane- 
polarized light, stained for calcite. 




tj(^. 



Figure 4.34: More extensive intergranular cracking in slide S-37. 1.25x magnification, cross- 
polarized light, unstained for calcite. 



Analysis and Observations 



Page 116 




Figure 4.35: A typical fractured, weathered Sheffield surface from sample 37. 7.5x magnification, 
fiber optic illumination. 




Figure 4.36: Digitized grain boundary image of 1 square cm of slide S-15. 



Analysis and Observations 



Page 117 




Figure 4.37: A surface grain detaching from the substrate on slide S-36. Thermally-induced 
deformation causes surface grains to fall off, opening microcracks that facilitate moisture 
penetration. lUx magnification, plane polarized light, stained for calcite. 




Figure 4.38: Etched surface grains oriented at various angles to one another on slide S-15. The 
random orientation of grains may contribute to thermally-induced surface damage in Sheffield 
marble. 5x magnification, plane-polarized light, unstained for calcite. 



Analysis and Observations 



JPagellS 





7 .^ w, ■v^^'JT 






/ -r 



K-i 



i 



Figure 4.39: Biological growth on the surface of the quarry sample, slide S-15. Fungi have 
digested the first 2 mm of the surface, creating a porous substrate. 20x magniflcation, plane- 
polarized light, stained for calcite. 



Analysis and Observations 



Page 119 



BIOQUANT ANALYSIS: SUMMARY OF DATA 



S-15 Weathered Sheffield Marble 


Average Grain Area (square microns) 


191,383 


Average Grain Diameter in Sample (microns) 


349 


Average Grain Perimeter (microns) 


1,471 


Average Grain Paris Factor 


0.56 


Number of Grains in 1 Square cm 


410 


Gradation Coefficient (So=^d75/d25) 


1.91 


Inequality Grade (U=d60/d10) 


4.70 



GRAIN SIZE SUMMATION 



Sieve Numbei 


Size (micronSj 


Number of Grains 


Percent 


200 


0-75 


2 


10.69% 


100 


75-150 





18.04% 


50 


150-300 


11 


23.16% 


30 


300-600 


21 


30.07% 


16 


600-1180 


31 


15.81% 


8 


1180-2360 


26 


2.23% 




>2360 


1 


0.00% 





s- 


15 Grain Size Summation 








n 




-] 




26% '' 


— — 




— 










!«■ 










20% - 


(^ 


- 




- — - — - 


Percent of Grains 














15% ' 




-" 




- — — -_ 




10% ' 


1 


- 






n 


-_ 






5". ■■ 


1 


~ 














0%. l- 


iL. 


1- 








n 






^'''° >2360 

Grain Size (microns) 



Table 4.4: Summary of Bioquant data and related measurements for slide S-15. 



Analysis and Observations 



jPageJ20 



ft 1 1 I M M 

cm 1 



Figure 4.40: A typical fresh Cherokee surface from sample 36. 



Fresh Cherokee 

The stone that is being used to replace the weathered marble at the Tweed 
Courthouse is texturally similar to the Tuckahoe marble and compositionally similar to 
the Sheffield marble. As such, it offers an interesting contrast to both. The two Cherokee 
thin section slides, G-26 and G-29, were taken from blocks of recently quarried stone. 
The highly crystalline surface of sample 26 is seen in Figure 4.40. The Cherokee marble 
exemplifies the importance of petrofabric and microstructure to weathering. 

Mineralogical Composition: Staining of both slides revealed the Cherokee 
marble to be almost purely calcitic. In thin section slide G-26, silica grains were 
observed to occur only rarely along the calcite grain boundaries. In thin section G-29, 
silica grains were observed to occur in larger amounts, but they still accounted for only a 



Analysis and Observations ^ *-?S£ 

small percentage of the overall composition. Figure 4.41 shows a typical section with 

calcite next to silica grains. 

Structural Characterization: The Cherokee samples are highly crystalline and 
are characterized by uniformity. Grains are all medium to large, with straight, strongly 
adhered grain boundaries. No preferred orientation of the texture was noted. The large 
grain size, as will be shown in the explanation of the Bioquant® analysis, is a factor that 
contributes greatly to the stone's documented resistance to weathering. Despite a lack of 
any noticeable preferred orientation, the large grain size, straight, angular grain 
boundaries, and extremely fine, almost fused grain-to-grain contacts seem to give the 
Cherokee a very strong texture. Figure 4.42 shows a typical section with large grain size 
and clean grain-to-grain contacts. 

Microcracks: At low magnification, the degree of microcracking in the Cherokee 
samples appeared to be low. However, at higher magnification, fine microcracking was 
indeed observable. Whether pre-existing due to recrystallization or resulting from 
quarrying processes, the microcracks were generally intragranular, as would be expected 
in a stone with large grains and strong intergranular cohesion. Figure 4.43 shows the type 
of microcracking common in the fresh Cherokee samples. 

Surface Fracturing: By analyzing a fractured surface of sample 29 under the 
stereoscope, it was observed that roughly 40% of the cracking was intergranular. The 
analyzed surface is seen in Figure 4.44. By looking at grains further below the surface 
of the thin section slide, the breakdown was closer to 75% intragranular cracking to 25% 
intergranular cracking. This was expected based on the observations about structural 
characterization. The large grain size and strong intergranular cohesion seem to 
determine the fracturing behavior in the fresh sample. The percentage of intragranular 



Analysis and Observations Page 122 

cracks observed, around 70%, would place it in the category of high to equivalent 
granular cohesion according to Grimm (1999). 

Bioquant® Analysis: Thin section G-29 was chosen to be analyzed in Bioquant . 
The digitized image of grain boundary outlines in 1 square cm of sample 29 is given in 
Figure 4.45. The Cherokee proved to be the largest-grained, most uniform of the 
marbles from the Tweed Courthouse. Only 91 individual grains were calculated in 1 
square cm. The average grain perimeter was 4 mm, significantly larger than the 
Tuckahoe. The average grain diameter was 0.94 mm, again larger than the Tuckahoe. 
The average grain section area was 977,018 square microns. Interestingly, the Paris 
factor was calculated to be 0.57, close to both Sheffield measurements. Additional 
calculations for grain size made with these data showed relative uniformity. 86% of the 
grains were larger than 600 microns in diameter. 30% of the grains were larger than 
1,180 microns in diameter. The largest category was for grains between 600 and 1,180 
microns in diameter, which accounted for 34% of the grains counted. 4% of the grains 
were 2,360 microns wide or wider. The gradation coefficient was calculated to be 1.87, 
and the inequality grade was calculated to be 4. 10. 

An individual summary of results for G-29 is provided in Table 4.5. A summary 
of all Bioquant data and related results for tested samples is given in Appendix 3. 

Decay Mechanisms: Very little decay was seen at low magnification. However, 
at higher magnification, etching of calcite was observed, as was incipient microcracking. 
The etching and microcracking mirrored the rhombohedral molecular structure of calcite. 
Figures 4.46 and 4.47 give some idea of how the weathering of Cherokee marble would 
progress in typical conditions of exposure. A block of Cherokee marble in the Stone 
Exposure Test Wall at the National Institute of Standards and Technology showed very 



Analysis and Observations 



Page 123 



little degradation after more than 50 years of exposure. Because of the large, very 
crystalline grains, there is relatively low porosity per volume of stone. The large polished 
surfaces of the grains equate to a low specific surface for moisture absorption and acidic 
decay. 




Figure 4.41: Crystalline calcite grains (red and orange) and silica inclusions (blue, purple, white, 
yellow). The silica occurs occasionally in the Cherokee marble. An unusually dense concentration is 
seen here. The silica forms both along the grain boundaries and within the calcite grains. 1.25x 
magnification, cross-polarized light, stained for calcite. 



Analysis and Observations 



Page 12 4 




Figure 4.42: Highly crystalline calcite grains in slide G-26. Note highly angular, fused grain 
boundaries. A siliceous inclusion, seen in blue occurs along the grain boundary towards the bottom 
of the photomicrograph. Twinning of calcite is also seen. 5()x magnification, cross-polarized light, 
unstained for calcite. 




Figure 4.43: Microcracking in fresh Cherokee slide G-29 seen at high magnification. Fractures follow 
the rhombohedral mineralogical structure of calcite. 40x magnification, plane-polarized light, 
stained for calcite. 



Analysis and Observations 



Page 125 




Figure 4.44: A typical fractured surface of Cherokee marble from sample 29. 4x magnification, 
fiber-optic illumination. 




Figure 4.45: Digitized grain boundary image of 1 square cm of slide G-29. 



Analysis and Observations 



P age 126 



BIOQUANT ANALYSIS: SUMMARY OF DATA 
G-29 Fresh Cherokee Marble 



Average Grain Area (square microns) 



Average Grain Diameter in Sample (microns) 



Average Grain Perimeter (microns) 



Average Grain Paris Factor 



Number of Grains in 1 Square cm 
Gradation Coefficient (So=<d75/di25) 



Inequality Grade (U=d60/d10) 



977,018 



943 



3,970 
0.57 



91 



1.87 



4.10 



GRAIN SIZE SUMMATION 



Sieve Number 


Size (microns) 


Number of Grains 


Percent 


200 


0-75 


2 


2.20% 


100 


75-150 





0.00% 


50 


150-300 


11 


12.09% 


30 


300-600 


21 


23.08% 


16 


600-1180 


31 


34.07% 


8 


1180-2360 


26 


28.57% 




>2360 


1 


1.10% 



G-29 Grain Size Summation 

35% 




Table 4.5: Summary of Bioquant® data and related measurements for slide G-29. 



Analysis and Observations 



Page 127 




Figure 4.46: Microscopic decay of fresh Cherokee sample number 26. Microcracking of surface 
grains gives some idea of what might happen on a larger scale when the replacement stone weathers. 
40x magnification, plane polarized light, stained for calcite. 



ikwi-.^ibiGMsa 




t... 



Figure 4.47: A block of Georgia Cherokee marble at the NIST Stone Exposure Test Wall in 
Gaithersburg, MD. After 50 years of outdoor exposure, the Cherokee block shows surface decay of 
less than a few microns. No staining from pollution was observed. The block is 2 ft. tall. 



Analysis and Observations i-5S£ 

Scanning Electron Microscopy 

Scanning Electron Microscopy (SEM) was applied to weathered and freshly 
fractured surfaces of Tuckahoe and Sheffield marble from the Tweed Courthouse as a 
complement to thin section analysis. As with the samples chosen for thin section, the 
samples used for SEM were picked because their identities were known. Sample 1 from 
the North Portico of the Kellum Section of the Courthouse was the source of the 
Tuckahoe images, and samples 36 and 37 from the south fa9ade were the sources of the 
Sheffield images. Both have been positively identified in the previous section of this 
chapter. The results of this analysis confirmed observations about microcracking and 
surface etching. In the case of the Tuckahoe sample, intragranular and intergranular 
cracking were seen on the fractured surfaces and large amounts of gypsum were seen on 
the weathered surface. In the case of the Sheffield sample, intergranular cleavage was 
seen and etching of surface calcite grains was also seen. 

Figure 4.48 shows the surface of the sample covered by platy gypsum crystals to 
such a degree that the marble grains themselves are not visible. The formation of calcium 
sulfate crystals on the surface is mirrored in the pores of the stone, where salt 
crystallization acts to further degrade the structure of the stone. Gypsum crystallization 
within the pores of the Tuckahoe marble has been shown in Figures 4. 19 and 4.21. 

On the fractured face of the same sample, characteristic intragranular and 
intergranular cleavage are evident, also confirming the previous observations. Figure 4.49 
shows this type of surface fracturing, common in the Tuckahoe. Energy Dispersive 



Analysis and Observations *-?§? 

Spectroscopy (EDS) showed the primary constituents of the crystals to be calcium and 
magnesium with sulfur also detected. Sulfur would be expected given the prevalence of 
gypsum on the weathered surface of the sample. 

A typical Tuckahoe inclusion is seen in Figure 4.50. A large dolomite crystal is 
surrounded by partial intragranular cleavage. The crystal is bordered on the bottom right 
by a micaceous phlogopite inclusion. 

The previous observations about the Sheffield marble were also supported by 
SEM analysis. A clear predominance of intergranular cleavage is seen on a fractured 
surface in Figure 4.5 1 . Fine cleavage is seen between very distinct calcite crystals, and 
very little intragranular cleavage is visible in the same image. The fine cleavage planes 
create a strong capillary absorption capacity in the stone. On the weathered surface, both 
etching of calcite grains (Figure 4.52) and an accretion of fine pollution or sediment 
(Figure 4.53) were visible. EDS confirmed that the primary constituents of the grains 
were calcium and oxygen. Appendix 3 contains the EDS readings. 

X-Ray Diffraction 

As with the previous analyses, samples were carefully chosen based on their 
known identity as either Tuckahoe or Sheffield marble. Two samples were picked for 
each category by visual comparison alone. Additionally two samples of Cherokee were 
chosen and another marble of unknown identity was also chosen. This marble was 
included because it was noticed to occur frequently on the building and could not be 
categorized easily as Sheffield or Tuckahoe based on a visual comparison. These samples 
were then pulverized and prepared for X-Ray Diffiaction. The results generally 



Analysis and Observations ^ ^^^e 130 

confirmed what had been observed in thin section analysis but also revealed something 
about the Tuckahoe's composition. 

The two Tuckahoe samples, 1 and 22, both from the North Portico, had interesting 
results. In sample 1, the characteristic peak for dolomite was observed to be double. Due 
to careful calibration, it was possible to determine that these corresponded to two 
varieties of dolomite (JCPDS# 36-0426 and #1 1-0078) containing different amounts of 
iron, 0.44% and 0.22% respectively, expressed as FeO. The increase in iron content 
shifts the dolomitic peak (d=0.288) to higher d-spacing reading (d=0.91) for the case of 
ankerite [Ca(Fe,Mg)(C03)2 ] (JCPDS#4-0586) with an FeO content of 19.15%. In 
sample 22, the intensity of these peaks was inverted, while in the common sample 41 
they were almost identical to Tuckahoe sample 1 . This would help to explain the iron 
spotting observed on the dolomite crystals themselves. A variable iron content may be 
characteristic of the Tuckahoe dolomite. The two Sheffield samples were identical, 
composed entirely of calcite. The Cherokee, as expected, was entirely calcitic. Test 
results and information about mineralogical identification are provided in Appendix 3. 

The Sheffield samples, 14 and 32, were identical. They were composed entirely 
of calcite, except for a small peak at 26.7 in sample 14. Cherokee, as expected, was 
entirely calcitic. Test results and information about mineralogical identification are 
provided in Appendix 4. 



Analysis and Observations 



Page 131 




Figure 4.48: Gypsum encrusted surface of sample 1. lOOx magnification, JEOL 6400 Analytical SEM. 



Analysis and Observations 



Page 132 




Figure 4.49: A fresh fractured Tuckahoe surface from sample 1. Jagged intragranular cleavage 
is seen to the right and top of the image and straight intergranular cleavage is seen in the center. 
lOOx magnification, JEOL 6400 Analytical SEM. 



Analysis and Observations 



Page 133 







Figure 4.50: Sample 1 surface with a distinct dolomite grain, center, adjoining a micaceous 
phlogopite inclusion, right. 50x magnification, JEOL 6400 Analytical SEM. 




Figure 4.51: Distinct calcite crystals on a fractured Sheffield surface from sample 37. Fine cleavage 
planes can be seen between grains. lOOx magnification, JEOL 6300FV Field Emission HRSEM. 



Analysis and Observations 



Page 134 




Figure 4.52: Etching of calcite grains on a weathered Sheffield surface from sample 36. Note the 
outline of an individual calcite crystal in the upper left hand of the image. lOOx, JEOL 6300FV Field 
Emission HRSEM. 




^""-■^W^. 



Sieafe;,;,, 



«9i|£.^ 



I <»'-', 












S^'j 










-3» 



Figure 4.53: Accretion of pollutants or fine sediment on the weathered surface of sample 36. The 
vague outline of a coated individual crystal can be seen in the center of the image. lOOx 
magnification, JEOL 6300FV Field Emission HRSEM. 



Analysis and Observations Page 135 

Comparison of Characterizations 

Finally, by comparing some of the observations made, it is possible to discuss the 
findings across the three stone types. Figures For instance, the average Paris factor of the 
Tuckahoe grains, 0.495, makes them the least circular in shape. The angularity and 
irregular boundaries of the Tuckahoe grains could translate into a higher toothing factor 
between grains, and hence a higher degree of intragranular cohesion. This is seen in the 
Tuckahoe' s grain cohesion categorization, equivalent to prevalent cohesion. Grain 
cohesion, a corollary of intra versus intergranular cracking is also affected by grain size. 
In the case of the Tuckahoe, the predominant grain size interval of 0.6 to 1.2 mm may 
relate to the amount of intragranular cracking seen. On the other hand, the high gradation 
coefficient and inequality grade may negatively influence the performance of the marble. 
The more inequally graded the grains are, the less likely it is that the marble will weather 

uniformly. 

In the case of the Sheffield, the smaller predominant grain size interval (0.3- 
0.6mm), higher average Paris factor (0.57) and lower gradation coefficient could 
contribute to the equivalent to subvalent granular cohesion seen in both fresh and 
weathered samples. The more distinct roundness of the grains, and hence the lower 
toothing factor, together with a small grain size would seem to make the Sheffield more 
susceptible to weathering than the Tuckahoe. This would also seem to be compounded 
by the anisotropic thermal expansion behavior of calcite, at least in areas of the building 
exposed to sunlight on a regular basis. Nevertheless, mineralogical content is an 
important controlling factor, as discussed previously. In reality, Tuckahoe and Sheffield 



Analysis and Observations Page 136 

may weather equally well or poorly, despite the differences between these observed 
factors, because of their very different mineralogical compositions. 

The highest gradation coefficient, 2.52, was noted in the Tuckahoe samples. As 
seen in the thin section slides, the Tuckahoe had a large number of medium grains but 
also a large number of smaller grains that contributed to a varied microstructure. The 
heterogeneous mix of grain sizes may contribute to different thermal expansion/ 
contraction behaviors. Because the grain sizes are more diverse, a greater specific 
surface is available on which acids can react. This could help to explain the stone's 
observed breakdown and friability, at least in the samples observed at the courthouse. 
The Cherokee turned out to be similar to the Sheffield in two categories: Paris 
factor and gradation coefficient. It was also closer to the Sheffield than the Tuckahoe in 
the category of inequality grade. Since it is compositionally so close to the Sheffield, it 
brings out several interesting points. Both the Sheffield and Cherokee are calcitic 
marbles, yet the Cherokee is noticeably more durable and is characterized by strong grain 
to grain cohesion in the fresh sample. The general gradation of grains between the two is 
almost identical. The main differences are the degree of crystallization, noticeably higher 
in the Cherokee, and the larger predominant grain size interval. These differences may 
largely explain the differences in durability between the two. 

Looking at the Tuckahoe, the lower average Paris factor would seem to predict 
better weathering than the Cherokee. Again, however, composition, gradation 
coefficient, and a high inequality grade seem to intersect with Paris factor to influence 
actual weathering behavior. In the Cherokee, lower specific surface makes moisture 
absorpfion more difficult 



Analysis and Observations 



Page 137 



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Table 4.6: Comparison of Grain Size Summation for the five marble types: G-29 Cherokee Fresh; T- 
8 Tuckahoe Fresh; T-IB Tuckahoe Weathered; S-38 Sheffield Fresh; and S-15 Sheffield Weathered. 
Grain sizes have been converted to logarithms of the actual grain sizes. Both Sheffield curves 
correspond to each other, as do both Tuckahoe curves. The Cherokee curve is noticeably distinct 
from the rest. 



COMPARISON OF DATA 



Marble Type 


Gradation 


Inequality 


Paris Factor Grain Cohesion 


Predominant 




Coefficient 


Grade 






Grain Size 




(So) 


(U) 






Interval 


Tuckahoe Fresh 


2.28 


5.1 


0.53 


equivalent to prevalent 


0.6-1.2 mm 


Tuckahoe Weathered 


2.76 


10.9 


0.46 


equivalent 


0.6-1.2 mm 


Sheffield Fresh 


1.75 


5.6 


0.58 


equivalent 


0.3-0.6 mm 


Sheffield Weathered 


1.91 


4.7 


0.56 


subvalent 


0.3-0.6 mm 


Cherokee Fresh 


1.87 


4.1 


0.57 


equivalent to prevalent 


1.2-2.4 mm 



Table 4.7: Comparison of gradation coefficient, inequality grade, Paris factor, grain cohesion, and 
predominant grain size interval across marble type. 



CHAPTER V 
Conclusion 

The observations made through thin section analysis of fresh and weathered 
Tuckahoe and Sheffield marble add to the previous observations about them. The 
juxtaposition of these two stones on the exterior of the Tweed Courthouse has 
provided architects and conservators in the past with an opportunity to look at the 
differential weathering of two superficially similar types of stone. In this instance, a 
relatively fundamental analytical tool, microscopic thin section, has been used to 
characterize the microstructure and breakdown of the two stones. This approach was 
suggested by the simple fact that thin section had never been applied in an extensive 
study of the Tuckahoe or Sheffield marbles and that it might yield useful information 
about each material's resistance to weathering. Sheffield marble has never been the 
subject of conservation analysis, making some sort of investigation into its behavior 
all the more worthwhile. The results of this study suggest that thin section was a 
useful method for understanding the makeup, behavior, and primary causes of decay 
of the Tweed Courthouse marbles. 

An interesting result of this research relates to the origin and mineralogical 
composition of the two types of marble used at the Tweed Courthouse. Historical 
records indicate that two quarries, or at least two distinct quarrying areas, provided 
exterior stone for the building. It has also been assumed in historical accounts that 



138 



Conclusion Page 139 

both types of marble were dolomitic. Testing by Ammann & Whitney and Mesick, 
Cohen, Waite has suggested that there were perhaps as many as seven different 
quarries based on observed compositional and mineralogical characteristics of the 
Tweed marble. This included an almost purely calcitic marble that may comprise as 
much as 30% of the exterior stone. The current research reconciles the previous 
accounts to some degree. 

Using samples carefully chosen from the exterior based on likely quarry 
origin, several important observations were made. First, it was confirmed that the 
Tuckahoe marble is indeed dolomitic. This was expected based on historic accounts 
and past analysis. Relative uniformity among the samples in thin section staining and 
XRD confirmed this general characterization of the Tuckahoe. Second, using a 
sample of marble recently taken from the Sheffield quarry as a benchmark, the 
Sheffield samples were identified as being highly calcitic rather than dolomitic. This 
was not expected. Again, relative uniformity among the samples in thin section 
staining and XRD confirmed the mineralogical characterization of the Sheffield. This 
finding points out the possibility that the Sheffield quarry could be the source of all of 
the calcitic marble seen on the exterior of the Tweed Courthouse. The Georgia 
Cherokee replacement stone was confirmed to be highly calcitic as well. 

In addition to confirming the Tuckahoe' s dolomitic composition and the 
presence of phlogopite and tremolite inclusions that affect surface weathering, it was 
also found that calcite grains occur regularly in the Tuckahoe samples. Due to the 
opposite thermal expansion behaviors of calcite and dolomite, this may be a 
determinant of weathering behavior in the Tuckahoe marble. On a structural level, 
the moderate to large grain size and moderately interlocking grain boundaries in the 



Conclusion Pagel40 

fresh samples would seem to predict low potential for thermal degradation. The 
marble Tuckahoe's mineralogical composition, heterogeneous grain size distribution 
and structure, and relative grain roundness would seem to additionally control these 
factors. Taken together, moderate to high potential for thermal degradation would be 
predicted in areas of the building that are exposed to regular thermal cycling. This in 
fact appeared to be the case with the weathered samples. 

On the thin section slides, many of the weathering phenomena that have been 
observed in the past were made vividly clear. The degree of gypsum crystallization 
within the microcracks, a factor that is known to accelerate decay, was well illustrated 
by photomicrographs of the weathered Tuckahoe. The presence of gypsum in the 
substrate derives from the layering of fine particulate pollution on the stone's surface. 
Calcium sulfate, formed from sulfurous pollution in the presence of water and drawn 
into the microcracks by capillary absorption, results in the presence of gypsum. EDS 
applied during SEM confirmed that the surface crystals were largely composed of 

sulfur and calcite. 

The unusual iron spotting of the dolomite, observed occurring on the dolomite 
grains themselves rather than within the stone pores, was also well illustrated by 
photomicrography, as were surface etching and the breakdown of the dolomite grains 
by sulfation. The shifting of the main peak in XRD seemed to confirm that the 
Tuckahoe dolomite crystals have some iron content, an observation that is worth 
noting since iron staining of the Tuckahoe is usually attributed to the presence of 
pyrite inclusions. These primary mechanisms of decay manifest themselves on the 
macroscopic level in extreme friability and discoloration, the dominant features of 
weathered Tuckahoe. 



Conclusion Pagel41^ 

The Sheffield's highly calcitic composition was the first and most obvious 
observation made, and it helps to explain some of the weathering phenomena seen in 
this type of marble. Because calcium carbonate is quicker to form calcium sulfate 
than magnesium carbonate is, black crusts of sulfurous pollution may be more 
commonly observed on the Sheffield blocks. It was also noted that grains of silica 
commonly occurred along the grain boundaries. Weak cohesion created by the low 
toothing factor between the silica grains and the calcite grains could contribute to the 
breakdown of the stone. This may be exacerbated by differential coefficients of 
thermal expansion and different anisotropic thermal expansion behaviors, 
contributing to deterioration, although these were not measured in this research. 

Other factors relating more strongly to microstructure seemed to be at work in 
the weathering of the Sheffield marble. For one, a large amount of intergranular 
cracking was observed even in the fresh Sheffield samples. The comparatively small 
grain size, straight grain boundaries, and relative roundness of the grains also 
predicted a strong potential for thermal degradation and microcracking in areas 
exposed to regular thermal cycling. The thermal anisotropic behavior of calcite, 
which controls the degree of damage due to thermal expansion, is an important factor 
in the early stages of decay. This appeared to be relevant in the weathered samples 
taken from the south fagade, which were characterized by a large amount of porosity 
due to intergranular microcracking and the subsequent loss of grain to grain cohesion. 
The capillary absorption capacity of the Sheffield resulting from this should be 
considered a major determinant of weathering. As seen in the SEM images, clean 
cleavage planes between individual crystals on the surface provide a direct entry for 
moisture and salts in solution. 



Conclusion 



Page 142 





Figure 5.1: Dutchman repairs to column flutes on Brooklyn City Hall. The one on the right is a 
closer match with the original Tuckahoe. After these repairs were made, extensive retooling was 
done to reduce the starkness of the contrast between the two types of marble. 




Figure 5.2: Cherokee replacement abacuses on a Tuckahoe capital. Although the difference 
between the two types of marble is noticeable and will become more distinct as the stone 
weathers, the mixture of Cherokee with the Tuckahoe and Sheffield has been limited to areas of 
the building where it will not be as noticeable. 



Conclusion Pagei43 

The introduction of Georgia Cherokee marble as a replacement stone adds 
another dimension to the differential weathering patterns of the past. Superficially 
similar to the Tuckahoe in grain size and general color, at least when the Tuckahoe 
has been cleaned, the Cherokee would seem to be a logical replacement. However, 
its greater durability and tendency not to discolor over time point out potential 
problems for the future. In planning the replacement of stone at the Tweed 
Courthouse, care is being taken to minimize this type of contrast. The architect 
overseeing the project originally specified that Cherokee replacement stone should be 
used mostly above the first floor and in the area of the cornice, out of normal viewing 
range. Due to a limited quantity of salvage and Sheffield quarried stone, the 
Cherokee is being used more and more on the lower parts of the building. 

Recent dutchman repair work done on columns at Brooklyn City Hall gives 
some indication of how the Cherokee will weather next to the Tuckahoe. Cherokee 
dutchman pieces were inserted into damaged pilaster flutes, and the resulting contrast 
was stark. When the Tuckahoe began to show discoloration, the contrast became 
even more pronounced. Additional tooling work was done to make the two stones 
appear more compatible. Figure 4.54 shows the difference between the Cherokee and 
the original Tuckahoe marble at Brooklyn City Hall. 

Elsewhere, the replacement of deteriorated exterior stone with a mixture of 
stone from the building and from the Sheffield quarry can be expected to produce 
familiar patterns of weathering. The reuse of this material raises a difficult question 
for conservators, that is, whether two stones with such a long history of repair 
problems and aesthetic incompatibility should be reused at all. 



Conclusion Page 144 

Such a large building with such a variety of conservation issues offers many 
opportunities for further research. Future testing could help to refine the data 
gathered in this analysis. One possibility for analysis related to this study would 
involve collection of fresh stone samples cut and quantified based on the their 
locations within the quarries. Careful notation of each sample's preferred orientation 
relative to the crystallographic x, y, and z axes would go a long way to producing 
more definitive data about microstructure and weathering. This approach has been 
used by geologists studying the behavior of marble as a building stone and has 
provided information that can be compared reliably across stone types. Given the 
nature of the samples used for this research, such measurements were not possible. 

Something that was not done in thin section analysis for this research is dot 
mapping in SEM of specific elements in the slides. Dot mapping could refine an 
understanding of the phenomena observed in thin section, such as iron staining, salt 
crystallization within pores, and the mineralogical identity of inclusions. 

Although there is little chance that such a program could be implemented at 
the Tweed Courthouse any time in the near future, testing for an appropriate 
consolidation treatment would also be an interesting area of research. The possibility 
of applying a barium hydroxide urea treatment to the stone has been explored in the 
past. A survey of consolidation treatments would broaden the range of options for 
dealing with the very friable weathered marble at the Tweed Courthouse. 

Another type of analysis that could be worthwhile is a facade by facade 
breakdown of stone types correlated to their degrees of deterioration. Mapping decay 
relative to position on the building and stone type would yield useful information 
about weathering as it is controlled by microclimate. Sufficient historical information 



Conclusion Page 145 

exists that such a project should be possible. This may be a suitable application for 
Geographic Information Systems. 

As the Tweed Courthouse ends its 140'^ year, the question of how to approach 
its stabilization for the future has become central. Although the courthouse is a 
building of broad historical scope and grandeur, any approach to its conservation and 
repair must begin and end with an understanding of it on the most minute scale. A 
failure to comprehend the fundamental mechanisms of weathering will lead to a 
failure to find an appropriate treatment. This thesis has attempted to contribute to the 
body of knowledge about the Tweed Courthouse by exploring the relationship 
between microstructure, composition, and decay of the exterior marble. It is hoped 
that it will assist in any future efforts at restoration or repair. 



Appendix 1 



Page 146 




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Page 150 



BIOQUANT ANALYSIS: SUMMARY OF DATA 



S-38 Fresh Sheffield Marble 

Average Grain Area (square microns) 1 68,726 

Average Gram Diameter in Sample (micr 358 

Average Gram Perimeter (microns) 1 ,548 

Average Gram Pans Factor 58 

Number of Grains in 1 Square cm 449 

Gradation Coefficient (So =-^d75/cl25) 1 75 

Inequality Grade (U=d60/d10) 5,60 



T-8 Weathered Tuckahoe Marble 

Average Grain Area (square microns) 407,500 
Average Gram Diameter m Sample (micr 522 
Average Gram Penmeter (microns) 2,345 

Average Grain Pans Factor 0.53 

Number of Grams m 1 Square cm 207 

Gradation Coefficient (So=-Jd75/d25) 2.28 

Inequality Grade (U=d60/d10) 5.10 



S-15 Weathered Sheffield Marble 

Average Gram Area (square microns) 191 ,383 
Average Gram Diameter in Sample (micr 349 

Average Gram Penmeter (microns) 1 ,47 1 

Average Gram Pans Factor 0,56 

Number of Grains m 1 Square cm 410 

Gradation Coefficient (So=-Jd75/d25) 1 91 

Inequality Grade (U=d60/d 10) 4,70 



G-29 Fresh Cherokee Marble 

Average Gram Area (square microns) 977,018 

Average Gram Diameter m Sample (micr 943 

Average Gram Penmeter (microns) 3,970 

Average Gram Pans Factor 0,57 

Number of Grams m 1 Square cm 91 

Gradation Coefficient (So =^d75/d25) 1,87 

Inequality Grade (U=d60/d10} 4.10: 



T-1 B Weathered Tuckahoe Marble 

Average Gram Area (square microns) 590,318 
Average Gram Diameter m Sample (micr 586 

Average Gram Penmeter (microns) 3,046 

Average Gram Pans Factor 46 

Number of Grains in 1 Square cm 145 

Gradation Coefficient (So =^d75/d25) 2,76 

Inequality Grade (U=d60/d 10) 1 ,90 



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-„_^,,,-,ii,T.i«s.-B,i«^g5;s^S!'»s«S!"ss;"»!5'-'!Sss^ss;£ssss8ss^;s£sssK;;a5iSsss3afiS?.s8;5ssgs = s 

'i|pip?liiiip.?ir¥i^p5ii-iil|-5S||p|p§iiss|s- 



































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1- 
























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;2Sg2SsSiiggsgIg«sSs;iSsg^gs3Sgss»ggs.g»s||sgs|88ssg»5ggisgl;sS 



gSSBRSSg 



!sSl<iS8!3W£:;SaSS = E¥Cg85SSSSSC!CRSS?iaS«8: 



!;~sis;sSsfe 



R'-'- 



?S8Hia = ?!SSaSSaa6ftS336SS = ts;;£aS 



= ~ "--""~~gS£«ig8Sg5SSKS8i^SI5S5ie3SS§3gs£SgiS«giS£iSs5SKfeggsiiilssi 



aagg 



f s 1 1 1 g 8 1 B II ** 5 









8 2 3 a * a s s s a K s 



^SSri^kn-sui'i'Wy.uio 



RS««SS-. ES!'S=;"a2RS2S = ;5!3!3SffiS;sa;5Sf:E = g 






i^iaiiiiii'8PiS-S§58~g|Sp§|S|SpSiS£Pi'"Sp8S8|Sp5SgS£i||isSpS§S|?SSi 



8-38328? 



;e8;sS^SRSS!'!SS3?; £SSS«S«SS8F;'.S-8 



^§sgSsi§ssg-8g¥ige5|s^ag5B5Rasg|ass2a;sg;5§ 






ac::"-';RS8s;s's&Kss"SS3s 
sjgasggss 



8i58Bssa«ssss8ffi3 = |sggSgasssgsgsgSsg53S|j.|g|s5g|R;"gi^|s;5S^|s£ 



Appendix 3 Page 154 






s " - ' s S ? s " ^ s s s a , 

QOOCJ C3. OOOOOO OOOOOOO OO OO O OOOOO DO ooooooooooo ooDoooaoaooooooooooocjaooooooooo 

,. ,|^l^--_lj^,...j5s£5gg5S'^8gSSK55^RlS|5g-«g3S5^52aSs£K5i5gas-^SffiRSSS5S«S3«g^ 

S8s8S = csa3SSSsf!S8!«:ss;;£ = Ssass°s«^S25e5S = »sC5»tjs-»iS8«Ssc;s«S5;sssss«a£8Rs3fi!2;sc;:in?jS!:;a:! 

SS^3SS2SEffS8!!<!S3SSft5B3ga5SS-''*°*SSSS8BRRiS£5SSSf;S!SS2S5SCffSSR818S6ISSlSol«R«;SSSS£SSS;:BSSSS 
R5Sa9«a50aS832SSa3CSRfe2l<lSSK2S: 5S|g2::SaS*t5«;sS!SaSC;5SIBSsSSSa58ISa = 2SSSffS5flgss8S!aiSsSs2 
a|!SIPJ£figjt;f)tSS3SSas8::S?;8S3S2 SS?3"8sa8ESi;;S»S2S82fi8eSSR2aE3§8SaFlfKSSSSsSslSSa§SRsi3 

ss!e£ss«sa«5ss«csB«SRSRsasisK.88s3 = acissxis5SKSc;°sssR;ss[sBffissasisaRss«fta»32gaii!s 

ooo d a a aoQoaooooooooooooooocjo ooooaoo o o oooooodoooooooooo o o oaooooo 

»s«BiS!SSss^S3-SRSSSsswaf;c^;:3SSs:?$i;s;5if;sff^rs5S:c!sss;Rj;ssa5as"aRS5r'C!;sssRss 

5S8aS»sSaSS»i2S2S2P;SaSRSSKia8sS»2aSi3RK9aSHR::8S»SSeSSiS£8SR26ls-;!SsS«ft8«SS 

5SRS!S^«S!C88Ss»sssase;:;;cass2sss-sKi«ssS3R;ss3sFiassfj?;sssssiaffas8S£ssBr»saass 



ssasS"sici«casg3sKS8S'^i8"S'isssa8saffi5ss5i(!«s'»"Ss;«KSi;iaffcC33asicsffi6ccfi:ap:RS»sss"3Bccai;5«ffs 

a O OOOOC30C3 DC3 O O C3 OOOOOOOOOOOOcacj ooo OOOOOOOOOOOO ooo OOOOOOOOOOOOOOQOOOOOOOOOOOOO 

5|^S|Si|glg§B"g|3»§i|5Si!ia|iBSg«»5SSp|||p»|§sSg!!"giSi«pg§|gS|i«SS|Rg^ 

fi?.isS$s8SS3SS§3SRS§«s8-^*5'''3S!8g5RS8t£a&'S-. [,'isssa«ft5ii5SSi;wa2;;RaR5e2S5sSa5a;a8ssaPi5i&gRs 
'''SsiiliKSgS''isi?-S55g^l3Sig855;*5ffis|39fi5saRaR8W2|isg5R;sSs 88S2 

S3&SaJStSa53ac«a8SWS*!S;SS£gSS^»5Sffi»;;SR:'35ff5E:!9«ftSES3S3S39ffi«iSSS58fi*aRSf^Sf^95S-S 
OQoaoooooooooooo OO OO OO oooooooooo o ooooooooaoooooooooooooaoQaoociooooooooooo 

51s§J5®SiSSSsipipi||ffi^Sspgpp3ER|s8sgsgsag«Rggs^|||2§gjSjs^H|R2 

astc:sssi«K2a;RS-st?«^£R28«««2;;saffi::;:;;a3srfeast;3S2S35aas!sffia8S!88a38ss;5a«i<!;Kiae = aa«aR;Ss;2 
«|g£Ss;assg!5Si§g»sc;ES?.ggggffiga;§5R^«-ggs5;§g3eRi8s«R52s|pi3£sia"ISS8Si£'S-»s««SS"R§2sg»§ 

5S»issK3S-;;«;88 8aasss«cst5;oasSRasssS5as«2ss:-'ssssS3a?. ;"s;:'S8S582p;2RW";^S5RS;j;«;saaff£S£ = a 

igsislil§S|SSgSSgg|i||sg|=||SsspS6Rg35|iggBaa5B«s5|aSS 

sSsgl"? "8'95-t = a|5s = S9i<iS = ;5-R««-sS-2SR2'' s23 |i«S5SS-ai:gSRS«ggs;25s'*'"-|-a5scigt"s| 



Appendix 3 Page 155 



cffEf:;;s(30sERa3asa»sR!B5enis85ffiscFj«iRsss«33ssPia5ss;ffl 



3a»s3S5;8;;a:sS2 = e2»SR5B«;ss;tp:cs8 = cs«55ises3BSR 



sssffifflssajsssgissssjsssffSsissRtssstnssSsswssSKsi'!^ 



c;3;affisssissffSftffis£3sasaffi35sK»ss»c«RS5tssss:affssPiRsas3SE;sc^isasEsa = = 8assisci'!SS^9sSK6»Rssss 

oo oaoQ ooooaooooooooooooooooooaooooo oo ooo oo ooooooooooooo C300oaaoc30Dacsooooooo 

^^CT^J^»/>^^"^^^'^1^^^^l^OO^^fif^^u^O^c0■^ ■vu^'-riotioo-vt^ ix)or<r^o>r>*fnoh* 5»r^r^<omto^--Or^ trio^mjji^a»r^r^Coi^ — ^c^^^co — coo^tT'O'NoO — O — CT'OD^ifliOiS 

:=S2!C5Sgff53Sa!S;S«R53S!RSS = Ri;3RS£i;S;SS3asS8!3SRl;S:SE!SSHS«S3SS!8!IB:!5 = °SRSSSSS;;8i'8S-35S3R:!S<! 

e89ffs^sBSffiRs;;«s;acssssC!8s = s8S8ssf;ssss«3Kas^;R£S«3!3SsaaaS5issffS eaf;c;Rsa"Ssass;s = 98SSS 

^lA^-r-^mrj^h^iOCTii^CTt — 'nnLOO^ — LO^f^-fl — mmmr^m ^mlOto^^ff»^w^r^CT^^^^^^ol^^oaDOT^ ^^h*^if>^nmi/itDr^CT^^fN^o^C30iflo^o^r^ *-^.^p^mm•■rD^ncD^O^flf^l^^^*0^'* 

S!i':!!S5::S5;8SItS5a£»Rna9S««BKa5«SS8KSffi3i5g8»SS3SSaSS2E5StRsaa8S2i ^SSKSSasSESaSsgKSSSIsa 
Csa2S8S8tiSsae»;;&SS8i8&5'a8S'-SBSSa;'K8«R5giSQe3KaS8K RSSSHSSRRsa sssssjssSt 

a»ci;Bgsa9sw;S'"Sesaasaa3R38sisa = si!;asi«£C9ffS59csssst«5SsasssE£sHasc;cas8ss»ssai2si'!is39»9Kcas 

0C3O0 oooooci ooD OO ooooooooooooooociooooooooooo ooo ooo oooooooooooooooooooooooooooo 

3Sffla|assaPssgs^39Ci33a-^Ra5B8c:»ss:sssstsBSi3S39f59ssEssaisass!BR8'ssss9jt!ss;;8sssfJaa5sa«ci = 

3 s wa s;!i!S2cs8as3s;;;2s2;::ssasns86s«cRa8 = ;affi«88R8ss;9SRswssss«nsK»sRS3i8856srj;Rsi<ia5Si;sis 

= SSaB«s-S-3ffpiKc;i«sgsS863 = §ff3a!sgsasass8s5asBS8si5«3ass| 

;^aRS'»^aa»^^gg*'>'s s;sSsR-s'gsffl|»iR|'-5!^s-'^^5s*5!"g»s^Rga2Sc:as|aRS<"-[s as g2|RS!sc:H = siilii s 



Appendix 3 



Page 156 

























































































































































































































































































































































































































































































































































































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s;sst'=«8s'" = £2^:::8SS«i2!sss3i"iai<!SffissS!:?3affr5;;;«;«^affi3Sss = ssas!Di'!s3S3SoS:;85ffS!8!s-iiiRsss««sssi'i!C 



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'SSS- Slas-SsfeasssasswsgBaReaaaSSsSaSgi 
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Appendix 3 Page 157 































































































































































































































































































































































































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ooooooooooooo oooooooooooo oooooooooooooooooooooooooooooo oooooooo o ooooooo oooooo 

wss8aBa9S3S£sasT5i8is£S[si«2;«as£8iS3aisaie;gs8aa = s2!<!sssR"sss3i«8sss£«5c;sa«s;5i'i2«86!88SRsSffs::3 
SS5'''-3:S = R2S-:22-''2 "= 2'"awf;H22'5»aftS*'"'-''''"S-a2HH = iS"a«SKsa'"Eft38'~s«"3Sffi = S'~i«Si'!s»9R":sS 



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Appendix 3 



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Appendix 4 



Page 163 





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nm mi iistihg 

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PL« I-HHa I!-S?ACE KRlLl IrCPSi FWHH 

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2 23.181 1.53^2 5.77 417.0 O.Vil 

5 26. 74a J.3330 14.35 1U57.0 D-Ha 

4 2"?. 466 i.2474 2.6i 192.0 0.040 
5 27.461 3.Z4SC 9.29 S71.3 D.lw 
S 29.530 J.O^ I'K'.OO "^aiS-G 0.207 

7 31.592 2.5321 J.il 275.0 0.2C0 

5 36.113 2-4S73 9.5i 687.a O-Ufi 
9 36.655 2.4514 2.42 175,0 0.047 

10 J9-54J 2.2791 13,84 ICOO-C- C.225 

11 43,312 2.DB91 13. &5 762.0 3.262 



Appendix 4 



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PEAi-S riLt LLSri»G 



my "Tit: :'t976.FIG 

s»yj=LE iDtifimaiic*: 

STEP 5122; (I.O^J 

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Appendix 4 



Page 168 



DATA FTLI: 116975. FSS 

sAMPLt ij£ai:::cArioji: 
Sim iJtttA: 2':.'JX' 

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7 36.072 2.4500 bM 412.0 0.1i8 
S 39.550 2.2"8T a.5i b21-0 0.272 
9 42. SM 2. 1135 2.65 192.0 i>.2S0 

10 43.295 2.':i% 6,c5 4«3.l' 0.267 
I ' peak rsiSt is less xiian step uidtri 



Appendix 4 



Page 169 




0009 



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PDJ.S niE LISTIK 

DATA FTlr: ;it:«7T.PKS CuU.FaFI- 'Ji i2-l4».2-ul A= 15:43:59 

SAKFLE lDDfIiriCAnC«: 113FC CC««OC« 41 

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PEAK 2-T3E?A >3PACI TiREI.; Ii'CPSi ?i«0« 

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2 25.035 3.12S1 3.21 375.0 O.'DIO 

3 2':'.52< 3.0256 JO. "7 192.0 0.276 
( 30.974 2.5a"2 ICO.OO 45t'^.0 0.229 
5 31,240 2.8.632 36. iC' 1667.0 0.260 
i 33.520 2.6735 4.20 152.0 -3-2*0 
7 33.749 2.6b58 6.02 2V5.0 0.139 
B 35.373 2.53"2 5.93 271.0 0.300 
9 3". 480 2.3996 4.34 221.0 0.260 

10 3«.4W 2.340? 3.3" 1S4.0 a.UO 

U 3y.Sbu i'.27Sl i.74 ;7:.0 0.25*3 

12 41.140 2.1942 10. 5o 483.0 5.1:40 

13 41.260 2.18S1 9.02 412.0 O.'M 
14 44.8*1 2Mn S.67 }?i:.0 0.2*0 

t ' pesk FWHM is less tbaa step wiiSth 



Appendix 4 



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X-RnV: 0-20 keU Window : None 
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Real: 96s 38"^ Dead 





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BIBLIOGRAPHY 



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Index 



Page 184 



Ammann & Whitney, ii, vi, 23, 24, 25, 
36, 37, 43, 44, 45, 46, 47, 48, 49, 71, 
155, 193, 197 

6 

Bioquant, xiii, xvi, 80, 81, 87, 88, 94, 
96,98,99, 109, 113, 114, 117, 120, 
130, 132, 133, 134, 139 

Briggs, John R., 11, 12 

Brooklyn City Hall, 158, 160 



calcite, 75 

thermal anisotropy of, 74 

thermal expansion of, 75 
cast iron, 26 

D 

dolomite, vii, viii, ix, xii, 35, 36, 45, 
57, 58, 59, 76, 85, 86, 87, 88, 89, 90, 
96,99, 100, 101, 102. 105, 106, 107, 
142, 143, 147, 156, 195, 197 
thermal expansion of, 75 

E 

Eidlitz, Leopold, viii, 16, 20, 21, 22, 

29,30,31,44,54,83,86,95,96, 

101, 102 

criticism of, 22 

style of, 20 
Energy Dispersive X-Ray 

Microanalysis, vi, 43, 50, 51, 52, 71 



grain size distribution, 151 

inequality grade, 152 

microcracking of, 132 

mineralogy of, 131 

structure of, 132 

XRD, 143 
grain boundary, vii, viii, x, xi, xii, 4, 

40, 42, 77, 78, 80, 86, 87, 90, 93, 96, 

97,98,99, 104, 108, 112, 113, 116, 

120, 127, 133, 136, 137 
grain size, xiii, 4, 42, 58, 61, 77, 78, 

79,80,89,96,97, 112, 113, 119, 

132, 133, 149, 150, 153, 156, 157, 

159 
gypsum, vi, 38, 47, 48, 49, 52, 55, 56, 

58,59,61,68,69,71,99, 100, 141, 

142, 156 



H 



Harper's Weekly, 6, 14 
Harper's Weekly, 9 



intergranular, viii, x, xi, xii, 73, 79, 87, 
92,97,98, 112, 114, 119, 121, 125, 
132, 133, 141, 142, 146, 149, 157 



Julien, Alexis, 38, 39, 40, 54, 73, 76, 
196 

K 

Kellum, John, 16, 18, 19, 20, 22, 25, 
27,30,45,54,61,83,86,95, 110, 
118, 140 



Georgia Cherokee marble, ii, xi, xii, 
xiii, xiv, XV, 2, 3, 78, 82, 84, 131, 
132, 133, 134, 135, 136, 137, 138, 
139, 140, 142, 151, 152, 155, 160 
Bioquant data, 133 
characterization of, 120 
decay mechanisms of, 134 
fracturing of, 133 
gradation coefficient, 152 



Lee marble, vi, 1, 41, 42, 55, 61, 65, 

66 
Little, Thomas, 16, 18, 19 

M 

marble deformation, 74, 75 
Merrill, George, 39, 40, 41, 197 



184 



Index 



Page 185 



Mesick, Cohen, Waite Architects, 49, 
50,52,53,54,56,57,60,61 

microcracking 

intracrystalHne, 79 

N 

New York County Courthouse 

Construction, 8 
New York Times, 6, 1 1, 14, 18, 19, 22, 

24, 27, 28, 29 
NIST, V, vi, xii, xvi, 61, 63, 66, 134, 

140 



Paris factor, xiii, 80, 81, 88, 93, 98, 99, 

108, 113, 116, 120, 129, 133, 138, 

149, 150, 151, 152, 153 
phlogopite, vii, viii, x, xii, 45, 46, 58, 

59,86,90,91,96, 101, 102, 103, 

107, 142, 147, 155 



Scanning Electron Microscopy, xii, 

xvi, 5,43,45, 50, 71,81,83, 112, 

140, 142, 145, 146, 147, 156, 158, 

161 
Sheffield, 26 
Sheffield marble, 11, 12 

Bioquant data, 113, 120 

characterization of, 110, 118 

classification, 47 

composition, 45 

decay mechanisms, 1 14 

decay mechanisms of, 120 

fracturing of, 112, 119 

geology of, 34 

gradation coefficient, 152 

grain size distribution, 151 

history of, 27, 40 

inequality grade, 152 

iron staining, 62 

microcracking of, 112, 119 

mineralogy of, 1 10, 118 

SEM, 141 

structure of, 111, 119 

weathering of, 28, 64, 66, 69, 83 



XRD, 143 

sulfur, 38, 47, 48, 51, 52, 141, 156 



Tenth Census of the Unted States, 36, 

38,39,40,41,55,73, 196 
texture, 3, 4, 36, 38, 39, 41, 42, 69, 75, 

77, 88, 132 
thermal expansion, ix, 39, 74, 75, 76, 

88, 100, 105, 149, 150, 155, 157, 

198, 199 
thin section, vii, viii, 2, 4, 5, 72, 78, 

79. 80, 81, 82, 83, 84, 85, 86, 87, 88, 

89,96,97,98, 104, 111, 112, 113, 

119, 122, 131, 132, 133, 140, 143, 

150, 154, 155, 156, 161 
toothing factor, 81, 149, 157 
Tuckahoe marble 

Bioquant data, 88, 97 

characterization, of, 85, 95 

chipping of, 62 

classification, 47 

composition, 45 

decay mechanisms of, 88, 99 

fracturing of, 87, 97 

geology of, 34, 36 

gradation coefficient, 152 

grain size distribution of, 88, 98, 
151 

gypsum, 100 

historical description, 35 

history of, 17,37,39 

inequality grade, 152 

John Masterton, 15, 27, 37 

microcracking of, 97 

mineralogy of, 85, 86, 96 

phlogopite and, 101 

SEM, 141 

structure of, 86, 96 

weathering of, 28, 38, 39, 6361, 64, 
68 

XRD, 143 
Tweed Courthouse 

architecture of, 16-23 

cast iron, 26 

cleaning of, 53 

construction timeline, 26, 27, 29, 30 



Index 



Cost of, 14 
Greek Revival, 17 
history of, 6, 7, 13, 15 
structural description, 23, 24, 26 
weathering of, 28, 149, 150 
Tweed William Marcy, 10, 1 1 
Briggs Quarry, 1 1 
Career of, 10 
Tweed Ring, 13 



Page 186 



U 

United States Capitol, 16, 37 

X 

X-Ray Diffraction, xvi, 5, 43, 45, 47, 
48,50,57,59,71,81,83,99, 155, 
156 



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