Flameware

by Ron Propst

This article first appeared in Studio Potter, Volume 2, Number 2 (Winter 1973/74).
(Note that company addresses and phone numbers may have changed since that time.)
Copyright © 1974 by Studio Potter. All rights reserved.
May be reproduced with permission of Studio Potter.

My interest in flameware first began when the stoneware body I was then using showed a disappointing inability to remain ovenproof. No matter how I changed the formula, casseroles continued to break. This caused great grief to me, and to my customers too. I became determined to produce a type of pottery which would adapt to temperature changes gracefully.

Today my feelings remain the same. Considering the amount of technology presently available, studio potters should be able to produce a ware sufficiently stable to be capable of standing up under severe conditions of direct-flame thermal shock.

My first experiments in flameware were involved with the use of petalite. My work with this body was very brief, due to the Rhodesian embargo which halted shipments of petalite. The following are some comments on my general findings on the use of petalite in flameware bodies.

Most flameware bodies consisting of approximately half clay and half petalite work well. A higher percentage of fire clay and less of ball clay seems to be the most durable. If a flux is needed to seal the clay body, talc seems to be the best. I cannot include a list of such workable formulae, due on my part to lack of testing and general use of petalite bodies. There is, however, a little-known current American supplier of petalite, who will, I understand, also send samples for testing:

Charles B. Chrystal Co., Inc.
53 Park Place
New York, NY 10007

As soon as petalite became generally unavailable, I began work with a local mineral called spodumene. Spodumene is quite different from petalite. It is higher in lithium and iron oxide and lower in silica. Moreover, it has a strange talent: at 1700F, the crystalline form of spodumene expands instead of shrinking.

In my first test with spodumene this trait became evident. The early tests involved using 50% spodumene and 50% clay. The clay body expanded about two inches and sealed the ware to the kiln shelf above. While chipping at the kiln shelves, I decided that something needed to be changed. Not only did the body expand a great deal, but it was left very porous. It was like high-fire bisque ware.

The next series of tests was involved with using pyrophyllite and spodumene. Pyrophyllite is a low-grade mineral (an aluminum silicate) mined in North Carolina. It is used primarily in wall tile bodies where it deceases thermal expansion. I felt that the clay body needed an increase in alumina content, and pyrophyllite would give the increase needed. This helped a great deal with the expansion problem, but the body was still quite porous.

Since that time I have revised the body at least twenty times. The following formula is the clay body I have used for the past five years. It is successful with different types of ball clay and fire clay. I am not sure how the body would measure up on a dilatometer (a machine which measures thermal expansion), but it has been successful for me and a number of other potters around the country. Pottery made of this body has successfully been used on top of gas and electric stoves.

Ron Propst's Flameware Formula
Spodumene (200 mesh)30
Pyrophyllite (200 mesh)10
Feldspar (200 mesh)10
Ball clay (OM#4)20
A.P. Green Fireclay30
Western Bentonite2
Macaloid1

It is very important to use the right type of spodumene. The best spodumene is mined by Foote Mineral at Kings Mt., North Carolina. For information on its chemical analysis and cost write:

Foote Mineral Company
Route 100
Exton, Pa, 19341
(215) 363-6500

It is the lowest in iron and highest in alumina content that I have tested. Lithium Corporation of America, Box 795, Bessemer City, North Carolina 28016, also produces spodumene, but it is very high in iron content, which I found unacceptable. The problem of iron content is very hard to overcome due to the fact that the iron is chemically combined in the crystal. This makes useless the removal of iron by the magnetic process.

Foote Mineral is now producing a low-iron spodumene for the glass industry, but it is not ground in mesh sizes for use in a clay body. This low iron spodumene would enable one to produce a light gray-to-white clay body. (The fired color of my flameware body is orange-to-deep-red-brown.) They are also producing a calcined spodumene which I feel has great potential in lower temperature flameware bodies.

The pyrophyllite used is called Pyrotrol 200 mesh, and comes from:

Piedmont Minerals Company
PO Box 7247
Greensboro, North Carolina 27407
(919) 292-0947

I used Kona A3 feldspar in the flameware body up until it was discontinued. Since that time we have been using K-200, a feldspar mined by the Feldspar Corporation of America, Kings Mt., North Carolina. I have found it to be an excellent substitute. The body seals up a little more, but I have found no adverse conditions in the flameproof qualities.

My reason for using Old Mine #4 ball clay is for its color. It is very light-burning and is as plastic as any ball clay I have ever used. I feel sure any ball clay would work as well.

The fire clay is dry-milled A.P. Green fireclay. It seems to be plastic enough, and I am interested in its large particle size, which I feel is important in this flameware body. We have used other plastic fireclays, but I found them unacceptable in the fired results. The clay body seals up more than necessary and the clay body lacks the terracotta appearance which it normally has.

No matter what clay formula you might come up with, the word MACALOID is an essential. Macaloid is a chemically-combined Hector Clay, used in industry as a suspension agent in lotions. In a clay body it is the greatest little plasticizer I have ever used. Because the flameware body has too little clay, some type of super-plastic material is essential to make it workable. Macaloid is the answer.

Macaloid is produced by National Lead Company. For information write:

TAM Division
Box C, Bridge Station
Niagara Falls, NY, 14305

It is also being sold by some major ceramic suppliers. It is a very expensive material, but worth every penny.

You must remember that the information in this article is only a staging point for anyone becoming interested in flameware. I use this formula because it has been most serviceable for me. I feel sure that innumerable clay bodies can be developed from this basic formula. For instance, if the clays used are more refractory, use more flux; if the opposite, decrease the flux.

It is important to realize that the glaze used on flameware is as important as the body. My experience shows that glazes with 15 to 25 per cent spodumene or lepidolite will generally work well on flameware. Many other glazes, especially high alumina glazes, will also work. Here are some basic formulae:

#1 Flameware Glaze     c/9-10
(White with red flecks)
Lepidolite32
Dolomite25
Whiting3
Talc3
Gerstley Borate2.5
Kaolin25
Flint9.5

#2 Flameware Glaze     c/9-10
(Orange to white)
Potash Feldspar6
Spodumene4
Dolomite4.5
Kaolin5
Whiting0.75
Tin Oxide1
Addition of 2% Cobalt Carbonate gives a nice blue.

#3 Flameware Glaze     c/9-10
(Brown to green)
Dolomite12.4
Whiting1.6
Potash Feldspar10
Kaolin12.8
Flint2.8
Cobalt Carbonate0.2
Red Iron Oxide0.4

Any glaze you use will change its image on flameware due to the large amount of flux in the body. This will make most glazes more fluid, and tones out most colors. I enjoy color in my glazes, which leads me to fire flameware at just about cone 9 or 9 1/2. This allows the glazes to be less fluid and does not burn the color away. My glaze firings, moreover, are reduced very little due to the fact that we found the carbon deposits under the glaze to be damaging. They will cause the glaze to begin popping off the surface of the ware after several months of use.

During firing any protruding parts, such as skillet handles, must be supported. The body becomes so fluid during the end of the firing that it is capable of oblonging itself, Those handles which are light-weight will need no support.

I hope these remarks will enable you to make a start with flameware. They come from my own personai experience, and while I am not a trained technician, flameware has been an interest of mine for a number of years. A great deal of help was given by Foote Mineral Company and the Lithium Corporation of America. If you have an interest in lithium compounds, these people are more than willing to help and supply samples.

Cast kilns
Flameware pot by Ron Propst (photo by Evon Streetman).

Ron Propst lives and works in Penland, North Carolina.