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North Carolina Sfafe Library 
*<•£ Raleigh 

North Carolina 
Department of Conservation and Development 

R. Bruce Etheridge, Director 

Jasper L. Stuckey, State Geologist 

bulletin Number 40 

manufacturing china clay 





D° c North Carolina 

Department of Conservation and Development 

R. Bruce Etheridge, Director 

Jasper L. Stuckey, State Geologist 

bulletin Number 40 

manufacturing china clay 





<***, *«* library 



Governor J. Melville Broughton, Chairman Raleigh 

Santford Martin, V ice-Chairman Winston-Salem 

Harry Bailey Spruce Pine 

Oscar Breece Fayetteville 

Bruce Cameron Wilmington 

K. Clyde Council Wananish 

W. J. Damtoft Asheville 

J. Horton Doughton Statesville 

Irving F. Hall ■_ Raleigh 

Roy Hampton Plymouth 

J. L. Horne, Jr j Rocky Mount 

William Carl Hudson Morganton 

Charles H. Jenkins P Aulander 

Paul E. Jones Farmville 

Carroll P. Rogers Tryon 

Richard Tufts Pinehurst 

R. Bruce Etheridge, Director 



Letter of Transmittal 5 

Foreword :::_:;: 6 

Introduction l 7 

Description and Location of Mineral Deposits 7 

Typical Analyses of Spruce Pine Alaskite 10 

Present Kaolin Deposits 10 

Analyses of Refined Kaolin Samples 11 

Available Supply of Kaolin 11 

Refining Kaolin 13 

Electric Firing 15 

Bureau of Mines 17 

Resistor : 17 

Results of Electric Firing Tests 19 

Rate of Firing 19 

Economics of Electric Firing 21 

Comparative Energy Costs 21 

Availability of Furnace 24 

Present Southeastern Market 24 


Figure Page 

1. Index Map Showing Location of North Carolina 

Kaolin Deposits 8 

2. North Carolina Residual Alaskite Kaolin Deposits 9 

3. Mine of Kaolin, Inc., Spruce Pine, N. C 12 

4. Plant of Kaolin, Inc., Spruce Pine, N. C 12 

5. A Mine of Harris Clay Company, near Spruce Pine, 

N. C 14 

6. Clay Preparation Machinery, Harris Clay Com- 

pany Plant near Spruce Pine, N. C 14 

7. A Feldspar Plant in North Carolina . 16 

8. Electric Periodic Kiln at Electrotechnical Labora- 

tory of U. S. Bureau of Mines, Norris, Tennessee- 18 

9. Casting Room at Electrotechnical Laboratory of 

U. S. Bureau of Mines, Norris, Tennessee 20 

10. Electric Tunnel Kiln at Electrotechnical Labora- 

tory of U. S. Bureau of Mines, Norris, Tennessee— 20 

11. Test Ware Produced Experimentally at TVA 

Ceramic Laboratory. Made Exclusively of 
North Carolina Kaolins and Other Domestic 
Materials 22 

12. Test Ware Produced Experimentally at TVA 

Ceramic Laboratory. Made Exclusively of 
North Carolina Kaolins and Other Domestic 
Materials 23 


Raleigh, North Carolina 
May 1, 1941 

To his Excellency, Hon. J. Melville Broughton, 
Governor of North Carolina. 

Sir : I have the honor to submit herewith, as Bulletin 
No. 40, a report on china clay manufacturing opportuni- 
ties in North Carolina. For many years, many have held 
the opinion that the manufacture of china clay offers 
advantages in our State. 

This report summarizes investigations and research 
directed toward leading the way to the exploitation of 
the mineral resources of the State which are the raw 
materials of the industry. It is hoped that this 
publication will give information which will be helpful 
in bringing new manufacturing enterprises to North 

Yours respectfully, 

R. Bruce Etheridge, 


The present report entitled "Manufacturing China 
Clay Opportunities in North Carolina" has been pre- 
pared to set forth in brief, the possibilities of producing 
high-grade ceramic products from local materials in 
Western North Carolina. The report is not the work of 
any one person but rather represents a summary of the 
field investigations and laboratory research carried on 
by the Tennessee Valley Authority and the United States 
Bureau of Mines over a period of several years. These 
investigations were greatly facilitated by the friendly 
cooperation of the various operators of the Spruce Pine 
District and adjoining areas. 

The investigations summarized in this report indi- 
cate that North Carolina contains large reserves of 
minerals and materials, to which only a minimum 
amount of accessory clays need be added in order to pro- 
duce high-grade ceramic wares by modern methods. The 
close proximinity of these accessory clays to the large 
reserves of North Carolina raw materials and the ex- 
istence of a ready market in the Southeast suggest 
splendid opportunities for the establishment of an in- 
dustry in Western North Carolina based on the utiliza- 
tion of these resources. 

Jasper L. Stuckey, 
State Geologist. 





An ample supply of fine china clay is found in the 
Spruce Pine District of North Carolina. Of special 
interest to the ceramic industry is the extremely low iron 
content and the occurrence of only a trace of titanium 
in the kaolin. An exceptionally fine grade of kaolin is 
now being produced for the china clay trade by two 
modern refining plants and several older plants located 
near Spruce Pine, North Carolina. This kaolin is also 
being used for various fillers and special products. 

Although kaolin has been produced from the Spruce 
Pine Area for more than a half century, its potentialities 
are not yet generally recognized, and the purpose of this 
booklet is to acquaint ceramic manufacturers with the 
possibilities of manufacturing chinaware in the south- 
east close to supplies of raw material and tapping an 
under-developed but growing retail market. 

Description and location of Mineral deposits 

These kaolin deposits have been formed from huge 
bodies of coarsely crystalline, white granite, ALASKITE, 
containing practically no iron-bearing minerals. The 
Spruce Pine alaskite has its greatest development in the 
vicinity of Spruce Pine, Mitchell County, North Caro- 
lina, and outcrops at irregular intervals over an area 
of about 225 square miles. The largest unbroken body 
occurs two miles northwest of Micaville, Yancey County, 
North Carolina, and has an outcrop width of about one 
mile and a length of about two and one-half miles. 
Occasional small Spessartite-like (manganese-iron) gar- 
nets are found in the alaskite, but hornblende is entirely 


Manufacturing China Clay Opportunities 

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In North Carolina 








10 Manufacturing China Clay Opportunities 

absent. Biotite, the high iron mica, is rarely found in 
the alaskite, although frequently associated with the 
pegmatite cutting the alaskite. Most granites and 
pegmatites contain various titanium minerals, but the 
Spruce Pine alaskite is an exception in that it contains 
no noticeable titanium minerals. 



No. 1 No. 2 
Percent Percent 

Si0 2 73.96 74.30 

A1 2 3 15.77 15.50 

Fe 2 3 0.33 0.30 

CaO 1.30 0.90 

K 2 3.74 4.56 

Na 2 4.57 4.15 

Ignition Loss 0.31 0.26 

Total ."_ 99.98 99.97 

The analyses of Table I are from the Minpro Labora- 
tory, United Feldspar and Minerals Corporation, Spruce 
Pine, North Carolina. 

The deposits are outstanding in the uniformity of 
the mineral content. All the alaskite bodies are essen- 
tially of the same composition and texture and are 
remarkably uniform throughout their extent. The pro- 
portions of feldspar, quartz, and mica vary only slightly 
within the bodies. The alaskite referred to in Table I 
contains 45.3 percent plagioclase feldspar, 2.12 percent 
microcline feldspar, 28.6 percent quartz, 2.2 percent 
muscovite mica, 0.5 percent garnet, 1.2 percent clays, 
and 1.0 percent other minerals. 


More than 50 geographically separate kaolin deposits 
associated with the Spruce Pine alaskite, have been found 
in Avery, Mitchell, and Yancey Counties, North Carolina. 

In North Carolina 11 

The largest and best of these residual deposits occur 
under terrace levels produced by the North and South 
Toe Rivers and Crabtree Creek. Practically all of the 
deposits contain recoverable kaolin and rarely occur with 
objectionable mining features, such as excessive over- 
burden and inaccessible locations. The beds are easily 
mined either by mechanical means or by water jets under 
moderate pressure. One deposit near the town of Spruce 
Pine is reported to have been mined to a depth of slightly 
more than 100 feet. 




No. 1 No. 2 

Percent Percent 

Si0 2 47.94 46.18 

A1 2 3 37.02 38.38 

Fe 2 3 -, - 0.60 0.57 

Ti0 2 0.02 0.04 

CaO 0.30 0.37 

MgO 0.07 0.42 

K 2 1.25 0.58 

Na 2 0.06 0.10 

Zr0 2 0.08 

Ignition Loss 13.03 13.28 

Total 100.29 100.00 

The analyses of Table II were furnished by Kaolin, 
Incorporated, and Harris Clay Company, Spruce Pine, 
North Carolina. 

Available Supply of kaolin 

It has been reliably estimated (1) that 51,000,000 tons 
of crude kaolin exist in Avery, Mitchell, and Yancey 
Counties, North Carolina. By crude kaolin is meant the 
kaolin and its accompanying matrix minerals less the 

(i) Paul M. Tyler and A. Linn: "Minerals Yearbook — United States Bureau 
of Mines. 1940." Page 1255. 


Manufacturing China Clay Opportunities 

Figure 3. Mine of Kaolin, Inc., Spruce Pine, N. C. 

Figure 4- Plant of Kaolin, Inc., Spruce Pine, N. G. 

In North Carolina 13 

schist and gneiss inclusions. The percentage of recover- 
able kaolin varies with the various deposits. Many de- 
posits have been worked on a 10 percent or greater 
recovery basis. A higher percentage than 10 percent of 
recoverable kaolin, however, occurs in many deposits. 

In addition to kaolin, these deposits yield valuable 
by-products from the kaolin refining process, such as 
high-grade muscovite mica used in the manufacture of 
roofing and as fillers, and semirkaolinized feldspar and 
quartz. The quartz is milky white, free from iron stains, 
and near the specifications for high-grade glass sand, 
although little use has so far been made of it for this 


In 1936, the Tennessee Valley Authority established 
a ceramics laboratory at Norris, Tennessee, to work out 
methods of refining North Carolina kaolin in order to 
produce all-American clay bodies suitable for the manu- 
facture of high-grade and medium-grade chinaware, and 
to replace imported kaolin. These experiments were car- 
ried out jointly with the U. S. Bureau of Mines and the 
Harris Clay Company of Spruce Pine, North Carolina, 
and in 1938 a new modern kaolin refinery was built in 
the Spruce Pine District. About the same time Kaolin, 
Incorporated, also of Spruce Pine, North Carolina, set 
up a large plant to refine kaolin by a process developed 
in Czecho-Slovakia. Both companies are now supplying 
a blended kaolin of uniform quality to the trade which 
is equal to the best imported kaolin. 

The TVA process is available to other prospective 
producers or manufacturers. Shipments of over 12,000 
tons of refined kaolin per year are now being made to 
northern potteries. 

In addition to the kaolin, there are potash, soda, and 
blended feldspars produced in the area which are used 


Manufacturing China Clay Opportunities 

Figure 5. A Mine of Harris Clay Co., near Spruce Pine, N. C. 

Figure 6. Clay Preparation Machinery, Harris Clay Company Plant near 

Spruce Pine, N. C. 

In North Carolina 15 

in the ceramic industry. This area contains the largest 
reserves of high-grade feldspar known in the United 
States, and has produced an average of 82,700 tons an- 
nually for the past decade. This material is produced 
by three large, modern grinding plants in the Spruce 
Pine area. One of these plants produces ground quartz 
in addition to the feldspar. It might also be of interest 
to the ceramist to know that the only pyrophyllite 
(H2AI2 (SiOs)4) mines and grinding plants in the United 
States are located in North Carolina. This industry is 
located in Moore and Randolph Counties, about 200 miles 
east of the Spruce Pine District, where three modern 
grinding plants are in operation. In these counties there 
are large reserves of high-grade crystalline pyrophyllite. 
Both foliated and fibrous or radiating varieties are 
abundant. Another important ceramic mineral in the 
Spruce Pine District is kyanite (ALSiOr.), which occurs 
commonly throughout most of the Mountain and much of 
the Piedmont sections of the State. The most important 
deposits are found on the western edge of the Spruce 
Pine District, in a belt 6 to 8 miles wide, extending from 
near Burnsville, Yancey County to Swannanoa, Bun- 
combe County. The mineral occurs in metamorphosed 
acid rocks and in pegmatite dikes and quartz veins, in- 
closed in these rocks. There are ample reserves of 
kyanite-bearing gneisses and schists which contain from 
5 to 40 percent of kyanite. A modern beneficiation plant, 
capable of producing a 98 percent kyanite concentrate is 
in operation near Burnsville. 


In order to test fully the use of North Carolina 
kaolins for high-grade dinnerware, the TVA built and 
operated at Norris, Tennessee, a small experimental or 
pilot plant in which was installed a continuous electric 
kiln. Different types of ware of good commercial quality 


Manufacturing China Clay Opportunities 



In North Carolina 17 

were made using domestic materials only and fired elec- 
trically. Kaolin from North Carolina was blended with 
that from Florida to give an ail-American all-kaolin 
mixture. A high-grade, vitreous, translucent dinner- 
ware was made in order to test thoroughly the best 
methods of blending the clay bodies and of molding and 
firing the ware. Best results seem to be obtained when 
approximately 12 percent of Florida kaolin or ball clay 
from Tennessee or Kentucky are added. The proximity 
of the Florida kaolins and the Tennessee and Kentucky 
ball clays to the Spruce Pine District make possible in 
this area the manufacture of an all-Southern body with- 
out the necessity of transporting these accessory clays 
great distances. 

bureau of Mines 

The Norris Ceramic Laboratory was recently turned 
over to the U. S. Bureau of Mines, who are continuing 
the experiments on electric firing and the development 
of southern raw materials for ceramic and other uses. 
The Bureau of Mines is also testing the production of 
large sanitary ware on a small commercial scale using all 
American materials under methods of electric firing. 

The Bureau of Mines reports that "The North Caro- 
lina kaolins correspond most closely of those tested to the 
English kaolins in physical and chemical properties, but 
as now prepared by improved methods, are finer grained, 
more plastic and stronger than English clays." 

The Bureau also reports that "North Carolina Alas- 
kite was found to represent a satisfactory and enormous 
potential source of white-firing, mixed potash and soda 
feldspar (plus flint) for many future generations." 


In order to retard oxidation and prolong the life of 
the heating element, the ceramic laboratory developed a 


Manufacturing China Clay Opportunities 


Figure 8. Electric Periodic Kiln at Electroteclmical Laboratory of U. 8. 

Bureau of Mines, Norris, Tennessee. 

In North Carolina 19 

graphite core resistor enclosed in a refractory tube of 
silicon carbide, in which hydrocarbon gas (propane) was 
held under a slight pressure. 

The latest tests on graphite resistors protected by a 
bonded silicon carbide tube, show a life of from 3,120 to 
4,872 hours of continuous firing and an average life of 
about 3,800 hours or about 6 months' operations. The 
use of these resistors is available under license for other 
purposes in the fields of heat treatment, metallurgy, 
electro-chemistry, etc. 

Results of electric firing tests 

The results obtained by firing large sanitary wares 
and masses of full size brick, substantiated by theoretical 
calculations, have shown that 

1. Radiated heat is the major method of transmis- 
sion at incandescent temperatures. 

2. Firing schedules similar to those in combustion 
fired kilns can be maintained by electric firing. 

3. Commercial requirements for quality and uni- 
formity of vitrification can easily be met if time 
is given for "soaking" or completing the reac- 
tions at the maximum temperatures. 

These results also substantially confirm the experi- 
ence in firing thin translucent dinnerware. 

RATE of firing 

High grade dinnerware has been bisque-fired satis- 
factorily in 18-hour cycles for the open setting to 36-hour 
cycles for plate bungs and heavy ware. The experimental 
kiln at the Norris Laboratory measures 55 feet long, 2 
feet and 11 inches wide, and 1 foot high to the spring of 
the arch (the kiln has two tunnels each with 1 foot by 1 
foot loading cross section), with a total of 14 heating 
elements, requires 85 to 110 kw. input, depending upon 
operating temperature, and has operated for over 8,500 


Manufacturing China Clay Opportunities 

Figure 9. Casting Room at Electroteclinical Laboratory of U. 8. Bureau of 

Mines, Norris, Tennessee. 

* c — -■"■ 


Figure 10. Electric Tunnel Kiln at Electroteclinical Laboratory of U. 8. 

Bureau of Mines, Norris, Tennessee. 

In North Carolina 21 

hours on all types of ware from fine china to face brick 
with ranges of temperature up to cone 14, 2550° F. The 
rates of firing used were faster than those now employed 
in the larger commercial, combustion-fired kilns, but 
these undoubtedly can be met in other small kilns. 


At present with electric energy at 2 mills per KWH 
the equivalent electrical energy consumed is comparable 
in fuel cost of natural gas at $0.58 per M feet, fuel oil 
at 8.4 cents per gallon, and coal at $16.25 per ton. 


100% 100% ratio to electricity 1 

Electricity Oil Gas Coal 

2 mill 8.40 580 $16.25 

100% 80% ratio to electricity 

2 mill - 6.70 46.50 $13.00 

3 mill 100 700 19.50 

100% 60% ratio to electricity 

2 mill 50 350 $ 9.75 

3 mill 7.50 52.50 14.60 

4 mill 100 70^ 19.50 

100% 40% ratio to electricity 

2 mill 3.40 230 $ 6.50 

3 mill 5.10 350 9.75 

5 mill 8.40 580 16.25 

Electricity : cost in mill per kwh = 3412 B.t.u. 
Oil : cost per gallon, 142,000 B.t.u. per gallon. 
Gas: cost per thousand cubic feet, 1000 B.t.u. /cu. ft. 
Coal: cost per ton, 14,000 B.t.u. /lb. 

i Different types of kilns operate at different degrees of efficiency. The 
above table gives cost comparisons for different efficiency ratios as com- 
pared to electricity. For example, in a kiln with an SO percent ratio of 
efficiency as compared to electricity, electricity at 3 mills per KWH would 
represent the same energy cost as fuel oil at 10 cents a gallon, natural 
gas at 70 cents per M feet, or coal at $19.50 a ton. 


Manufacturing China Clay Opportunities 

Figure 11. Test Ware Produced Experimentally at TV A Ceramic Laboratory . 
Made Exclusively of North Carolina Kaolins and Other Domestic Materials. 

Figure 12. Test 
Ware Produced 
Experimentally at 
T V A Ceramic 
Laboratory. Made 
Exclusively of 
North Carolina 
Kaolins an$ Other 
Domestic Mate- 


24 Manufacturing China Clay Opportunities 

Electric firing offers : 

1. The clean oxidizing atmosphere of the best muffle 
kiln designs. 

2. The most efficient methods of temperature con- 

3. The most efficient use of energy since there are 
no losses of heat from stacks nor radiation from 
open, exposed fire boxes. 

4. Possible savings in fuel costs in those districts 
having high oil or gas prices and low electricity 

5. The opportunity of using multiple tunnel kilns 
with more uniform distribution of heat units 
and greater savings. 

Availability of furnace 

The use of the electric tunnel kiln at Norris, Ten- 
nessee, is available to ceramic manufacturers desiring 
to conduct their own tests of electric firing. Electricity 
will be supplied by the TVA at standard commercial 
rates. Extra labor, supplies, repairs, and miscellaneous 
expenses of operation can be supplied at actual cost plus 
a small percentage for overhead and handling. 


Based on 1935 Census of Manufactures, the estimated 
annual market for whiteware in the nine southeastern 
states is $10,361,000, of which $9,770,000 worth is pro- 
duced outside the area. This includes not only china- 
ware, but sanitary and plumbing ware. 

The market for chinaware in the Southeast not cov- 
ered by production in the area and sold through depart- 
ment stores and five and ten stores is conservatively 
estimated to be about $3,325,000 annually.