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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
lA>tAir<^vQ
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.
Historical 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 Background 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.
Historical 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 Background 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
Previous Analysis and Cleaning
Page 59
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.
Previous Analysis and Cleaning
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.
Previous Analysis and Cleaning
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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 65
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.
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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
Page 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
Page 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
Page 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
Page 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
Page 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
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
Page 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
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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
0
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 11 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 124
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
Page 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
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.
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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
4.00
3.50
0)
N
3.00
c
5
2.50
o
«»-
o
2.00
£
£
*^
1 SO
(Q
O)
O
-J
1.00
0.50
0.00
0%
Grain Size Distribution
-G-29
-T-8
T-1B
S-38
-S-15
20%
40%
60%
80%
100%
120%
Percentage
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
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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 0 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 0 46
Number of Grains in 1 Square cm 145
Gradation Coefficient (So =^d75/d25) 2,76
Inequality Grade (U=d60/d 10) 1 0 ,90
Appendix 3
Page 151
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= SSaB«s-S-3ffpiKc;i«sgsS863 = §ff3a!sgsasass8s5asBS8si5«3ass|
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Appendix 3
Page 156
ii
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Appendix 3
Page 158
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Page 159
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Page 161
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Page 162
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Appendix 4
Page 163
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Appendix 4
Page 165
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Page 166
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Page 167
Appendix 4
Page 168
DATA FTLI: 116975. FSS
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Appendix 4
Page 169
0009
Appendix4 ^ P^g^ ^''^
PDJ.S niE LISTIK
DATA FTlr: ;it:«7T.PKS CuU.FaFI- 'Ji i2-l4».2-ul A= 15:43:59
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5 31,240 2.8.632 36. iC' 1667.0 0.260
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7 33.749 2.6b58 6.02 2V5.0 0.139
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9 3". 480 2.3996 4.34 221.0 0.260
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Appendix 4
Page 171
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Page 172
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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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