cone 10 cone 6

www.ceramicartsdaily.org | Copyright © 2010, Ceramic Publications Company | Making the Switch from Cone 10 to Cone 6 Ceramic Glaze Recipes | i

a little knowledge of ceramic glaze chemistry

and raw materials goes a long way

ceramic artsdaily.org

making the switch from

cone 10 to cone 6ceramic glaze recipes

www.ceramicartsdaily.org | Copyright © 2010, Ceramic Publications Company | Making the Switch from Cone 10 to Cone 6 Ceramic Glaze Recipes | 1

Mid-Range Reduction: It’s Not Just Cooler, It’s Coolby John Britt

There are a number of reasons why someone would want to fire at cone 6 rather than cone 10, but John Britt was not one of those people—until he was asked to present a workshop on the topic. His understanding of ceramic glaze materials and glaze chemistry helped him to quickly find a path from cone 10 firing to cone 6.

Cone 6 Crystalline Glazes: Developing Crystals at Mid Rangeby William Schran

Historically, crystalline glazes have been the purview of the high-fire potter. But like everything else, if enough people experiment and test, good results can be obtained under all sorts of circumstances - in this case, crystals at cone 6.

Traditional Cone 10 Glazes Make the Leap to Cone 6by Rick Malmgren

There are a lot of traditional glaze recipes out there, but they are typically formulated for firing at cone 10. Rick Malmgren has reformulated and adjusted many traditional ceramic glazes to function well as cone 6 glazes, and he has some compelling reasons to do so.

Making the Switch from Cone 10 to Cone 6 Ceramic Glaze RecipesA Little Knowledge of Ceramic Glaze Chemistry and Raw Materials Goes a Long WayIf you want to convert cone 10 glaze recipes to cone 6, you’ll need to know something about glaze chemistry and the materials that work best at those different temperatures. If you just want to start with established cone 6 recipes, which is often a lot easier, there are now many people who have done the research and testing so you don't have to. But don’t worry; there will still be plenty of glaze-testing fun for you to try in your own studio.

In Making the Switch from Cone 10 to Cone 6 Ceramic Glaze Recipes: A Little Knowledge of Ceramic Glaze Chemistry and Raw Materials Goes a Long Way, we present several successful examples of cone 10 glazes reformulated to work at mid range, and include explanations of the glaze chemistry behind these successes.


Mid-Range Reduction:It’s Not Just Cooler, It’s Cool

by John Britt

With all the current discussion about global warming and conservation, I thought I should relate a recent workshop I taught at MudFire Clayworks and Gallery, a community ceramic

art center in Decatur, Georgia, just outside of Atlanta. They offer studio space, monthly workshops and a beautiful gallery of contemporary ceramics artists. They also fire to cone 6 in reduction. Erik Haagensen and Luba Sharapan, the owners of MudFire, had started to fire cone 6 reduction because of a defect in the kiln they’d purchased, but after seeing the results they had no reason to change back, even after the kiln was repaired. Firing to cone 6 was cheaper, faster, and the results were almost indistinguishable from high fire.

The ProjectAlthough they fire to mid-range reduction, Erik and Luba

had read my book, “The Complete Guide to High-Fire Glazes,” and wanted me to give a workshop on the cost and time benefits of cone 6 reduction firing, as well as to explain the reasoning behind glaze recipes, firing cycles and to show them how to bring glazes from cone 10 down to cone 6.

I normally work with, and teach about, high-fire glazes (cone 9–11), approximately 2350°F (1288°C), while mid-

range, (cone 5–7), is about 2200°F (1204°C). Although this is only about a 150°F (66°C) temperature difference, raising the temperature 150°F at the peak of the firing takes quite a bit more energy and puts a lot of extra wear and tear on the kiln. It could easily take two to four more hours of firing to go from cone 6 to cone 10 with the gas on high, so firing to mid-range reduction would save considerable fuel if compa-rable glazes could be found.

At that time, I didn’t have a lot of experience with mid-range reduction and I found it hard to believe that the results were “almost indistinguishable.” I did have a good bit of experience firing mid-range oxidation in an electric kiln and the results are far from the look of cone 10 reduction. But the idea intrigued me, and the more I thought about it, the more I realized that the same principles of high fire reduc-tion should apply to mid-range reduction. The key question would be if the oxides and materials needed to melt the glazes at a lower temperature would negatively affect the glaze colors. So I took the challenge, reasoning that I could use the same research methods I used for the high-fire glazes to explore these mid-range glazes.

Mid-range firing in both oxidation and reduction is a well researched area dating back before the energy crisis of the

Thrown and altered platter, 12 in. (30 cm) in diameter, stoneware with Cherry Blossom Shino and Woo Yellow glaze, fired in reduction to cone 6, by Bar-bara Morgenbesser.


1970s. There are also several college clay programs that use mid-range reduction and have published their glazes. One notable example is Diana Pancioli, at the University of Eastern Michigan, who started her “Glaze Forward” program. (For a small shipping fee, you could send for a list of cone 6 reduction recipes and test tiles of those glazes.) There are also organizations like the Clay Studio in Philadelphia that fire cone 6 reduction and have developed a wonderful palette.

The ResearchMy first step is always completing an exhaustive survey of

known glazes from books, internet and workshop handouts. Luba and Erik generously sent me all their recipes from MudFire [see selected recipes on page 51], and I pulled out my cone 6 glaze notebooks and began assembling recipe lists and firing instructions.

There is so much information available today that it is almost paralyzing; you don’t know what to do with it all. So in order to make it usable, I organized the recipes into types, like iron glazes (celadon, temmoku, kaki, iron saturate, etc.), shino, copper red, oribe (copper green), magnesium matt, etc. Then, after eliminating all the duplicates, I looked for similarities and differences, and from those, selected enough

glaze recipes to test that would show a broad range of possi-bilities within a type. Then I tested those recipes in a variety of firing cycles, like heavy reduction, light reduction, early reduction, late reduction and oxidation. This way, I can reveal a glaze’s full potential.

Iron glazes are a great type to start with because you can see a wide range of colors by incrementally adding one colorant; iron oxide. For example, when firing in reduction using the same base glaze, adding 1% red iron creates a blue celadon, adding 2–4% iron oxide will give green to amber celadons, adding 5–10% iron oxide makes temmokus, and 10–20% iron oxide gives iron saturates. Teadust temmokus result from additions of magnesium carbonate to temmokus fired with cooling soaks. Kakis, which are also part of the iron glaze type, are obtained with additions of bone ash and magnesium carbonate. Finally, oil spots result from stiff oxi-dized temmokus with magnesium oxide. So you can see how one glaze type can show you a world of glaze colors.

Copper red glazes are generally low alumina and high al-kaline bases with small amounts of copper carbonate (0.3%) and tin oxide (1%). Oribe glazes use copper to get greens while magnesium matt glazes yield satin whites and purples with cobalt oxide. You can try to reproduce these “types” at various cones and, as always, you may then have to make adjustments after you see the results.

Mugs, 4 in. (10 cm) in height, stoneware with Temmoku Gold, gas fired in reduction to cone 6, by Luba Sharapan.

Noodle bowl, 4 in. (10 cm) in height, stoneware with Mal-colm Davis Shino Glaze, gas fired in reduction to cone 6, by Erik Haagensen.

Handbuilt vase. 8 in. (20 cm) in height, porcelain with Mint Julep Glaze, gas fired in reduction to cone 6, by Melissa Keen-Boggan.


JEFF’S RED Cone 10 Reduction

Barium Carbonate . . . . . . . . . . . . . 4 .4 %Dolomite . . . . . . . . . . . . . . . . . . . . 8 .7Whiting . . . . . . . . . . . . . . . . . . . . . 8 .4Zinc Oxide . . . . . . . . . . . . . . . . . . . 1 .7Frit 3134 (Ferro) . . . . . . . . . . . . . . . 8 .7Custer Feldspar . . . . . . . . . . . . . . . 41 .9Silica (Flint) . . . . . . . . . . . . . . . . . . . 26 .2 100 .0 %Add: Tin Oxide . . . . . . . . . . . . . . . . 2 .6 % Copper Carbonate . . . . . . . . 0 .5%. % Bentonite . . . . . . . . . . . . . . . . 1 .0 %

PANAMA RED Cone 6 Reduction

Dolomite . . . . . . . . . . . . . . . . . . . 7 .76 %Gerstley Borate . . . . . . . . . . . . . . 10 .67Strontium Carbonate . . . . . . . . . . 4 .17Whiting . . . . . . . . . . . . . . . . . . . . 2 .60Zinc Oxide . . . . . . . . . . . . . . . . . . 2 .60Custer Feldspar . . . . . . . . . . . . . . 44 .10Ferro 3110 (Ferro) . . . . . . . . . . . . . 9 .70EPK Kaolin . . . . . . . . . . . . . . . . . . 2 .60Silica (Flint) . . . . . . . . . . . . . . . . . . 15%. .80 100 .0 %Add: Tin Oxide . . . . . . . . . . . . . . . . 2 .62 % Copper Carbonate . . . . . . . . . 1 .75%. %

SHANER ORiBECone 10

Bone Ash . . . . . . . . . . . . . . . . . . . . 1 .1 %Talc . . . . . . . . . . . . . . . . . . . . . . . . 7 .9Whiting . . . . . . . . . . . . . . . . . . . . . 22 .1Custer Feldspar . . . . . . . . . . . . . . . 31 .0Kaolin . . . . . . . . . . . . . . . . . . . . . . 12 .6 Silica (Flint) . . . . . . . . . . . . . . . . . . . 25%. .3 100 .0 %Add: Copper Carbonate . . . . . . . . . 5%. .2 %

SELSOR ORiBECone 6

Gerstley Borate . . . . . . . . . . . . . . 12 .5%.0 %Whiting . . . . . . . . . . . . . . . . . . . . 10 .41Nepheline Syenite . . . . . . . . . . . . 5%.6 .25%.Silica (Flint) . . . . . . . . . . . . . . . . . . 20 .83 100 .00 %Add: Copper Carbonate . . . . . . . . 5%. .00 %

This is a test I made with Selsor Copper Red and I removed the colorants and added copper carbonate, so I called it Selsor Oribe .

COLEMAN TEADuST TEMMOKuCone 10

Talc . . . . . . . . . . . . . . . . . . . . . . . . . . 7 %Whiting . . . . . . . . . . . . . . . . . . . . . . . 16Custer Feldspar . . . . . . . . . . . . . . . . . 40Ball Clay . . . . . . . . . . . . . . . . . . . . . . . 12Silica (Flint) . . . . . . . . . . . . . . . . . . . . . 25%. 100 %Add: Red Iron Oxide . . . . . . . . . . . . . . 10 %

TEADuST TEMMOKuCone 6

Whiting . . . . . . . . . . . . . . . . . . . . . 10 .5%. %Frit P-25%. (Pemco) . . . . . . . . . . . . . . 26 .3Alberta Slip . . . . . . . . . . . . . . . . . . 63 .2 100 .0 %Add: Red Iron Oxide . . . . . . . . . . . . 5%. .0 %

Side By SideThe final type I concentrated on

was shino glazes. Shinos are generally made with varying amounts of feld-spar and clay. For example, you may have somewhere between 60–90% feldspar and 10–40% clay. A typical recipe would be 70% feldspar and 30% clay. This is the most difficult glaze type to reproduce at mid-range because most feldspars melt around cone 9 and then with the added clay it is hard to melt much lower than cone 10. I started by using nepheline syenite, which is not a true feldspar but rather a feldspathoid (containing less silica than a true feldspar). It melts around cone 6. Because it is high in sodium oxide and lower in silica, the effects are not identical, but it was a good starting point and worth a try.

FiringI loaded the kiln with these various

glaze types and then filled the re-mainder with line blends within these glaze types and a variety of other recipes, like blues, greens, yellows, blacks, etc., to see the overall effect of varying firing cycles across the board of glaze colors.

For the first firing, I started reduc-tion at cone 010 and kept it heavy (0.65–0.72 on the oxygen probe) to cone 6 at 3 o’clock (cone melting position, not time of day). I had pretty good copper reds and iron glazes but the shinos were dull and washed out. For the next firings, I increased the fir-ing temperature to cone 7 at 3 o’clock, which gave me about 25°F more and brightened up the glazes. I ran five more firings to this cone, including full oxidation, light reduction, medium reduction, heavy reduction and oxi-dation with reduction at peak tem-perature. I also tested glazes with flux variations too numerous to mention, exploring mid-range fluxes like boron oxide, sodium oxide, lithium oxide, calcium oxide and zinc oxide [see side-bar on page 50]. Adding fluxes and reducing alumina and silica affects the response of coloring oxides in glazes, so the trick was finding suitable colors in properly melted glazes.


Eggy Vase, 15 in. (38 cm) in height, John’s Shino with decoration using Amaco Velvet underglaze, gas fired in reduction to cone 6, by Erik Haagensen.

Mid-Range FluxesGlazes contain alumina and silica, which both melt at very high temperatures, so getting them to melt at mid-range temperatures requires different fluxes than at high-fire temperatures:

Sodium Oxide (Na20) is a strong alkaline flux and creates brightly colored glazes. It has a melting point of 1652°F (900°C) and a high expansion/contraction rate, which will often cause crazing in glazes. It is often found in association with potassium oxide in feldspars. Common mid-range sources include sodium feldspars (nepheline syenite—actually a feldspathoid—is the lowest melting feldspar and so it is often used at midrange. It is high in sodium and

NOte: Frits come in a wide range of types. They are used by industry as reliable and consistent sources of fluxing oxides in relatively insoluble form. They are relatively low in alumina and silica and are active melters, but they can settle rapidly.

lower in silica than other feldspars and melts around cone 6.), soda ash, wood ash, borax, frits and Gerstley borate or its substitutes.

Lithium Oxide (Li2O) is the lightest weight, smallest particle size and most powerful of the alkaline fluxes with a strong color response similar to sodium and potassium oxides. It has a melting point of 1472°F (800°C) and has a low expansion/contraction rate, which can cause shivering in glazes. Sources include lithium feldspars and lithium carbonate.

Zinc Oxide (ZnO) is an auxiliary flux in oxidizing atmospheres. It has a dramatic color response, both good and bad, depending on the colorant. It can heighten colors with copper and cobalt oxides, but produces dull colors with chrome oxide. It has a melting point of 3587°F (1975°C), but if it is fired in reduction it will change to the metal zinc

and volatilize at 1742°F (950°C). It has a low expansion/contraction rate, so it can help to reduce crazing. Sources include zinc oxide and calcined zinc oxide.

Boron Oxide (B2O3) is a glass former and a flux with a molecular structure similar to alumina. It melts at 1292°F (700°C) but begins melting at 572°F (300°C). It has a low expansion/contraction rate and produces good color response in glazes, with characteristic bluish, milky streaks and cloudy effects. Sources include Gerstley borate (or its substitutes like Gillespie Borate, Murray’s Borate, Laguna Borate, etc.), borax and frits.

ResultsThe results were great for copper reds and iron glazes, as well as

greens, blacks, blues and carbon-trap shinos, which were very nice in heavy reduction. The carbon trap shinos worked because they contain soda ash, which melts very early, and with early reduction the carbon is already “trapped” below the soda layer so the peak temperature is not a factor. The only glaze type I could not achieve was traditional shinos, as I had expected. And I only had limited success with oil spots in the gas oxidation trials. This was also to be expected as iron oxide only starts to self reduce at 2250°F (1232°C) and that is about the peak temperature we reached. Soaking at cone 7 helped, but they were not as spectacular as a cone 13 oil-spot firing. Nevertheless, we did get spotting and some promising oil-spot recipes.

From all this testing, I came to the inescapable conclusion that Erik and Luba were correct. Ninety percent of the mid-range glazes were indistinguishable from their high-fire twins. This leads us to ask, why don’t more potters fire to cone 6/7 in reduction?

Making the Switch There seem to be a few obstacles in getting potters to convert to the

idea of mid-range firing. First, there is the inertia of their current prac-tice. Change is hard in spite of the obvious benefits, especially if you have been doing the same thing for 20 years and it is working.

Also, there is an underlying belief, although it is completely incor-rect, that cone 10 is superior to mid-range or low-fire, and chang-ing this mind set is an educational challenge. I think that this comes from the long historical European search to imitate Chinese high-fire porcelain. The goal was always to achieve high fire, so it gained the psychological high ground.

When you mention mid-range, potters immediately think, as I ini-tially did, of mid-range electric oxidation. But this is not the only way


to fire mid-range. Mid-range reduction has a completely different look, as does mid-range oxidation soda firing or mid-range reduction soda firing.

And finally, when you mention firing to mid-range, potters immediately want to change or convert their cone 10 glazes to this lower temperature. This is perceived as a significant challenge because it means that they will have to learn a glaze calculation software and unity molecular formulation. Most just want recipes that work. They know it will take time and effort to learn to convert all these recipes and they just don’t want to spend their time doing that.

I don’t recommend converting glazes to the lower temperature, because when you lower the firing temperature of a glaze you are using different fluxing oxides that have different color responses. So although it is possible to convert your glaze to the lower temperature, you will end up with a different glaze anyway. It is better to use the many tried and true mid-range glazes already in use and test them in your cycle. This is the same way potters find high-fire glazes; they get glaze recipes from books or from friends and then vary the colorants and opacifiers.

Although change is hard, potters should focus on the benefits of firing mid-range reduction. First, as stated above, it saves fuel, reduces your carbon footprint and costs less. Second, it saves time. It may take 2–4 hours to get the extra temperature of cone 10 and maybe longer depending on the size of the kiln. So rather than firing for 10–12 hours you will be out in 8–10 hours. Firing to mid-range also reduces the wear and tear on your kiln, which means that it lasts longer. Finally, and most importantly, you get great results!

After all this testing, we discovered that the methods used to test high-fire glaze types also apply to mid-range types and, as a result, we found some very nice glazes. Erik, Luba and the potters of MudFire Clayworks are proof of that. Hopefully, this will help other potters get started firing to mid-range reduction.

the author John Britt lives in Bakersville, North Carolina, and is the author of the book The Com-plete Guide to High-Fire Glaze: Glazing & Firing at Cone 10. For more information and to see John’s work, go to www.johnbrittpottery.com.

Tumblers, 7 in. (18 cm) in height, stoneware with Gold Temmoku liner and Raw Sienna exterior glaze, gas fired in reduction to cone 6, by Erik Haagensen.

recipesJOHN’S SHiNO

(Cone 5%.–6)Gerstley Borate . . . . . . . . . . . . . . . 4 .9 %Soda Ash . . . . . . . . . . . . . . . . . . . 2 .9Nepheline Syenite . . . . . . . . . . . . . 5%.4 .5%.Spodumene . . . . . . . . . . . . . . . . . . 22 .8OM 4 Ball Clay . . . . . . . . . . . . . . . . 14 .9 100 .0 %

MALCOLM DAViS SHiNO(Cone 10)

Soda Ash . . . . . . . . . . . . . . . . . . . . . . 16 %Kona F-4 Feldspar . . . . . . . . . . . . . . . 9Nepheline Syenite . . . . . . . . . . . . . . . 39Cedar Heights Redart . . . . . . . . . . . . . 6EPK Kaolin . . . . . . . . . . . . . . . . . . . . . 17OM 4 Ball Clay . . . . . . . . . . . . . . . . . . 13 100 %

CHERRY BLOSSOM SHiNO(Cone 6)

Soda Ash . . . . . . . . . . . . . . . . . . . . . . 10 %Nepheline Syenite . . . . . . . . . . . . . . . 40Spodumene . . . . . . . . . . . . . . . . . . . . 40EPK Kaolin . . . . . . . . . . . . . . . . . . . . . 10 100 %

RAW SiENNA(Cone 6)

Wollastonite . . . . . . . . . . . . . . . . . . . . 28 %Frit 3195%. (Ferro) . . . . . . . . . . . . . . . . . 23Nepheline Syenite . . . . . . . . . . . . . . . 4EPK Kaolin . . . . . . . . . . . . . . . . . . . . . 28Silica (Flint) . . . . . . . . . . . . . . . . . . . . . 17 100 %

Add: Red Iron Oxide . . . . . . . . . . . . . . 6 % Rutile . . . . . . . . . . . . . . . . . . . . . 6 %

MiNT JuLEP(Cone 6)

Gerstley Borate . . . . . . . . . . . . . . . 2 .9 %Magnesium Carbonate . . . . . . . . . . 2 .9Whiting . . . . . . . . . . . . . . . . . . . . . 22 .4Frit 3124 (Ferro) . . . . . . . . . . . . . . . 8 .8Nepheline Syenite . . . . . . . . . . . . . 22 .7EPK Kaolin . . . . . . . . . . . . . . . . . . . 20 .3Silica (Flint) . . . . . . . . . . . . . . . . . . . 20 .0 100 .0 %

Add: Red Iron Oxide . . . . . . . . . . . . 1 .0 %

WOO YELLOW(Cone 6)

Dolomite . . . . . . . . . . . . . . . . . . . 15%. .41 %Strontium Carbonate . . . . . . . . . . 23 .90Nepheline Syenite . . . . . . . . . . . . 42 .5%.0Kaolin . . . . . . . . . . . . . . . . . . . . . 9 .04Silica (Flint) . . . . . . . . . . . . . . . . . . 9 .04 100 .0 %

Add: Zircopax . . . . . . . . . . . . . . . 19 .23 % Bentonite . . . . . . . . . . . . . . . 4 .76 % Epsom Salt . . . . . . . . . . . . . . 1 .19 % Red Iron Oxide . . . . . . . . . . 3 .5%.7 %

TEMMOKu GOLD(Cone 6)

Cornish Stone . . . . . . . . . . . . . . . 67 .41 %Dolomite . . . . . . . . . . . . . . . . . . . 7 .86Gerstley Borate . . . . . . . . . . . . . . 3 .37Lithium Carbonate . . . . . . . . . . . . 6 .17Whiting . . . . . . . . . . . . . . . . . . . . 8 .98Silica (Flint) . . . . . . . . . . . . . . . . . . 6 .17 100 .00 %Add: Red Iron Oxide . . . . . . . . . . . 11 .24 %


by William Schran

Cone 6 Crystals:Developing Crystals at Mid Range

My fascination with macrocrysta l l ine glazes began as a graduate student.

While visiting a local exhibition of an individual’s collection, I dis-covered two small porcelain bottles by Herbert Sanders. The glazes ap-peared to have blue colored snow-flakes frozen on a transparent sky of orange. From that initial en-counter, macrocrystalline glazing has become a process that I’ve re-visited many times over the years.

Sanders had published Glazes for Special Effects in 1974, which contained recipes for crystalline glazes. In 1976, I began experi-menting with several recipes listed in the book, but since it was dif-ficult to fire our electric kilns to the required cone 9–10 tempera-ture range, I had little success. An article by David Snair in Ceramics Monthly provided additional glaze recipes and techniques for prepar-ing the pots for firing. Though all the recipes were for cone 9, a comment in the article stated that

firing to cone 6 would also pro-duce crystals. I had some limited success with these glazes, but that comment stuck in my head.

Fast forward to 1994. Discus-sions of glazes with a group of my students lead to a question about crystalline glazes. This one ques-tion resulted in a semester-long series of glaze tests that resulted in few successes. It was the problem I had encountered years before, our electric kilns only reached cone 9–10 with much difficulty. The lack of success producing crystals by my students only strengthened my resolve to find a solution. It was then, that I recalled the Snair article and the comment about cone 6.

With additional information gathered through internet searches and interlibrary loans, I discovered some artists experimenting with crystalline glazes at lower tem-peratures. Since we conducted our glaze firings to cone 6 at school, I decided to target this tempera-ture for my testing. My initial

Four vessels, to 8 inches in height, thrown B-Mix clay.

Glazes are as follows. Left to right: Fa’s

Cone 6 Base (Revised) glaze with 3%

manganese dioxide and .5% cobalt

carbonate; MFE (Dan Turnidge Revised)

glaze with 3% manganese dioxide

and 1% cobalt carbonate; Fa’s Cone 6 Base glaze revised with 3% manganese

dioxide and .5% cobalt carbonate; and

MFE (Dan Turnidge Revised) glaze with

3% manganese dioxide and 1%

cobalt carbonate.


experiments involved firing cone 10 glaze recipes only to cone 6. These tests resulted in the discov-ery that crystalline glazes could be produced in this lower tempera-ture range by simply introducing additional fluxes. The flux that seemed to produce the best results was lithium carbonate. Other materials that would function as a powerful flux were either soluble or contained additional silica and alumina, which are not desirable in crystalline glazes.

All of my experiments with crystalline glaze firings, up until fall 2006, have been done in a manually operated electric kiln. The kiln has infinite controls, so with careful monitoring, I was able to control the firing sched-ule fairly accurately. A digital pyrometer is an essential tool to closely track temperature changes, especially during long holding cycles. Acquisition of my first kiln with a programmable controller has allowed for more complicated, repeatable firing schedules. The ability to be able to alter tempera-ture ramp speeds and specific tem-perature hold times has opened up new avenues of experimentation. I have also found that, for both types of kilns, a direct vent system is important for rapid cooling cycles and maintaining an oxidiz-ing atmosphere.

Crystalline TechniqueI’ve developed techniques through years of experimentation, adopting processes that worked, eliminating

those that produced only limited success. Web searches and recent publications provide a variety of approaches to this very involved process, and each individual needs to conduct tests to find the process that makes the most sense for his or her particular circumstances.

Crystalline glazes produce the best results when applied to a smooth white clay body. Many artisans work with a porcelain clay body. Porcelain comes with its own set of issues and I have found a cone 10 porcelaneous stoneware clay—B-Mix or Bee-Mix—that works very well with my glazes. I chose to use a cone 10 clay to reduce the amount of alumina that might be picked up by the glaze.

A normal glaze has a mix of silica/flux/alumina in a ratio that provides a glassy surface and remains in place when melted on a vertical surface. A crystalline glaze contains little or no alu-mina, which would inhibit crystal growth. The glaze is comprised of silica, flux and a saturation of zinc oxide. This highly fluxed mix of materials leads to a very fluid glaze and steps must be taken to avoid destroying kiln shelves or the kiln.

Catch Basins and PedestalsEvery pot must have its own catch plate/basin to contain the glaze that runs off the pot. The catch plate need not be made from the same clay as the pot. The plate can be wheel thrown or hand built. Each pot must also have some type of pedestal device to facilitate re


a mix of white glue, which holds the pedestal in place before firing, and kaolin, which acts as a sepa-rating agent after firing. Striking with a sharp chisel or heating with a small torch just below the joint with the pot removes the pedestal. After encountering a number of problems with each of these

Crystalline glazes run off the pot so you need to raise the piece on a pedestal that sits in a catch basin. it’s important to select a pedestal that closely matches the diameter of the foot. Preparing several sizes allows you to select one with the correct fit.

1

Apply three to four coats of glaze to achieve the desired thickness, brushing each layer in a different direction to ensure that brush strokes aren’t visible and you have an even coating.

2

Pieces ready to load in the kiln. Each glazed pot is positioned on a pedes-tal that is placed in a catch basin.

3

After the firing, the fluid glaze will have run down over the pedestal and into the catch basin.

4

moval of the pot after firing. Some potters use insulating firebrick to create the pedestal. The brick must be at least a 2600K-type and coated with kiln wash. Another technique involves throwing the pedestal from the same clay body as the pot. After bisque firing, the pedestal is attached to the pot with


The pedestal and catch basin are re-moved by tapping with a small chisel along the line where the pedestal joins the pot.

5

Excess pedestal material and glaze are ground off the bottom using a bench grinder fitted with a silicon carbide grinding wheel.

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WARNING Proper eye and respira-tory protection must be worn during this pro-cess. Do all grinding outside the studio, if possible.

materials and form the mix into ¾-inch thick “biscuits” cut to the foot diameter of the bisque fired pot using round cookie cutters. I’ve found this material to stand up well to the melting glaze and soft enough to be easily knocked off with a chisel. Any remaining pedestal is easily ground away from the pot.

Glaze ApplicationCrystalline glazes may be applied like most other glaze, but since I don’t have spray equipment or room in my studio to store large

i use a portable flat lap machine fitted with diamond grinding and smoothing disks to even out and smooth the bottom of the foot with 100 and 260 grit disks. Since water is used in this process, i do this in the studio, but still wear eye protection. Self-adhesive diamond disks or silicon carbide disks can be attached to plas-tic bats and the potters wheel used to grind and smooth the bottoms.

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methods, such as pots falling over or broken foot rings, I sought another solution. Ellie Blair, a fellow crystalline artist, provided this process to me—the pedestals are a mix of equal parts by vol-ume: alumina, kaolin and sawdust. Add just enough water to bind the


buckets of glaze, I apply crystal-line glazes by brush. Most of the time I mix a few hundred grams at a time, which is sufficient to glaze two or three small pots. Since the crystalline glaze contains no added clay to keep the glaze in suspen-sion, you don’t want to add just water to wet the glaze. To wet the glaze, I use a CMC gum solution by adding about two heaping tablespoons of CMC powder to one quart of hot water. I let the powder soak into the water for at least 24 hours. The soaked gum is then stirred, resulting in a thin honey consistency. I add this to the dry glaze, stir and pass through 40 mesh, then 80 mesh sieves. The wetted glaze should have the consistency of thick honey.

Apply the glaze fairly thick. I ap-ply one coat by brush horizontally around the pot. When that dries, I apply a second coat vertically, then a third coat in a diagonal di-rection to the upper ²/³ of the pot. Sometimes I’ll apply a fourth coat to the top.

On the interior of vase/bottle forms and on the exterior of bowls, I use a cone 6 stoneware glaze. I selected a glaze that fits my clay body to create a watertight seal. With a crystalline glaze on just the interiors of bowls, I don’t have to be concerned with pedes-tals or catch plates.

FiringPots, with their pedestals and catch plates, are loosely loaded in the kiln. In my 4 cubic-foot-kiln, I will have at the most a dozen pots. Avoid using too much kiln furniture. It takes more energy and

time to heat and cool kiln furni-ture than it does the pots. Always use witness cones in every firing. Even if you fire with a program-mable kiln and don’t look at the cones during the firing, they will be the best record of the firing. Keep meticulous notes of every firing. Keep a logbook of your fir-ings and cross-reference each glaze to its firing. Fara Shimbo and Jon Singer gave the best advice dur-ing a presentation at the Lattice Structures Crystalline Glaze Sym-posium in fall 2005: When you’re testing, change only one thing at a time. If you alter the glaze in any way, change only one amount or material at a time. Do not change anything else. If you alter the firing schedule, do not change the glaze until you see what change the fir-ing has made.

Should the pot come out of the firing with few or no crystals, take heart and give it another chance. If the glaze has not filled the catch plate, simply apply another coat of the same glaze or a different glaze and fire it again. Should the catch plate be filled with glaze, it will be necessary to remove the pot from the pedestal, grind the foot even and create another pedestal and catch plate. I have refired some pots up to five times before I achieved results that were to my satisfaction.

CleanupAfter the firing, knock the pedestal loose with a small chisel or screw-driver. Strike the pedestal material, not the joint between the pots and pedestal. I use a bench grinder


Bottle, 7 inches in height, thrown B-Mix clay, with Fa’s #5 (Revised) glaze with additions of 4% manganese dioxide and 1% cobalt carbonate.

fitted with a silicon carbide grind-ing wheel to remove any remain-ing pedestal material and glaze. I do all of my grinding outside and I always wear proper eye and respiratory protection. After coarse grinding, I use a portable flat lap fitted with diamond disks to even out and smooth the foot. Silicon carbide disks and diamond disks with self adhesive backing can be attached to plastic bats and used on the wheel to grind and smooth pot bottoms. Squirting or spraying with water while grinding will help keep down the dust.

Firing ScheduleUse one of the following firing schedules for cone 6 crystalline glazes. You will need to experi-ment to determine the best firing schedule for your kiln. The abil-ity of the kiln to respond to rapid heating and cooling ramps is a critical factor in successful crystal-line glazes. Kilns should be loaded loose, using as little kiln furniture as possible. Older, well-used ele-ments may not be able to keep up with programmed demands of the kiln. I’ve found heavy duty ele-ments begin to be unable to keep up with the programmed firing schedule after about forty crystal-line firings.

For Manual Kilns with Infinite Controln Turn on kiln to a medium setting and monitor closely.n Try to maintain the holding temperature for 3–4 hours.

n Low – ½ hourn Medium – ½ hourn High – cone 6 overn Turn off kiln, cool to holding temperature (1850°F–1880°F)

Each section of the kiln may need to have a different setting to maintain a constant temperature. For my kiln, a setting of #3 on the top and middle section, and “M” setting on the bottom section provided a fairly consistent reading.


Crystalline Base Glazes

MFE (Dan Turnidge Revised)

Cone 6Ferro Frit 3110 . . . . . . . . . . . . . . . . .5%.0 .0 %Silica (325%. mesh) . . . . . . . . . . . . . . .22 .5%.Zinc Oxide . . . . . . . . . . . . . . . . . . . .22 .5%. 95%. .0 %

Add: . . . . . . . . Lithium Carbonate 1–5%. .0 %

Fa’s Base (Revised)Cone 6

Zinc Oxide . . . . . . . . . . . . . . . . . . . .25%. .0 %Dolomite . . . . . . . . . . . . . . . . . . . . . .5%. .0Ferro Frit 3110 . . . . . . . . . . . . . . . . 5%.1 .0Silica (325%. mesh) . . . . . . . . . . . . . . .19 .0 100 .0 %

Add: Lithium Carbonate . . . . . . . . .2–4 .0 %

Fa’s #5 (Revised)Cone 6

Zinc Oxide . . . . . . . . . . . . . . . . . . . .27 .0 %Talc . . . . . . . . . . . . . . . . . . . . . . . . . 5%. .0Ferro Frit 3110 . . . . . . . . . . . . . . . . .5%.0 .0Spodumene . . . . . . . . . . . . . . . . . . . .4 .0Silica (325%. mesh) . . . . . . . . . . . . . . .14 .0 100 .0 %

Add: Titanium Dioxide . . . . . . . . . . . .2 .0 %

ColorantsAdd the following colorants individually or in combination:

Cobalt Carbonate . . . . . . . . . . . .0 .25%.–3 .0 %Copper Carbonate . . . . . . . . . . . 0 .5%.–6 .0 %Manganese Dioxide . . . . . . . . . . 0 .5%.–3 .0 %Iron Oxide . . . . . . . . . . . . . . . . . 0 .5%.–3 .0 %Rutile . . . . . . . . . . . . . . . . . . . . . 0 .5%.–3 .0 %Nickel Oxide . . . . . . . . . . . . . . . .0 .25%.–3 .0 %

For Programmable Kilns

n Hold at 2210ºF for 10 minutesn Cool down 750°F per hour to 2000°F, hold for 1 hourn Cool down 750°F per hour to 1900°F, hold for 3 hoursn Kiln off, vent off, total firing 9–9½ hours

n Increase temperature 350°F per hour to 700°Fn Increase temperature 750°F per hour to 2000°Fn Increase temperature 150°F per hour to 2210°F (this puts cone 6 over, cone 7 at 1 o’clock position)

Higher holding temperatures results in fewer but larger crystals with more ground (areas without crystals) exposed.

Note: My kiln uses an “S” type platinum thermocouple with the thermocouple offset turned off. Each kiln may indicate a different temperature when cone 6 bends over. Use witness cones and closely monitor them until the correct peak temperature is determined.


I have become a strong advocate of Cone 6 reduction firing in recent years. My reasons are as follows:• Lovely traditional glazes look as good as or better

fired at Cone 6 than they do at Cone 10. Copper reds, Shinos, temmokus and dolomite matts are virtually indistinguishable from their Cone 10 brethren. Some Cone 10 glaze recipes don’t even need to be adjusted—a few look just great at Cone 6.• Fuel savings amount to about 30% over a Cone 10 firing. Granted, that isn’t much per firing (only the cost of two coffee mugs per kiln load, as Pete Pinnell once said), but if you are burning $2000 worth of propane per year, as I was a few years ago, it amounts to a nice $600 bonus at the end of the year.• The savings in fuel costs is nothing, compared with the savings of time and energy. Being able to fire off a full kiln load in 7½ hours instead of the 10½ that it

used to take me is where the real savings comes in. At Cone 6, I can fire during the day and teach at night, on a more normal work schedule.• Though I’ve fired my kiln more than 700 times, each firing takes its toll. The hotter it is fired, the harder it is on the arch, the walls and the shelves. There is that much more expansion and that much more contrac-tion, and that much more slumping. Cutting the tem-perature saves all the way around.• Mountains of research have already been done for Cone 6 oxidation, resulting in thousands of recipes. Oxidation potters have had to work hard with for-mulation to bring vitality to their glazes; they can’t depend on the atmosphere to do the work for them. Many of those same recipes fired in a reduction kiln are simply dazzling.The following are my favorite recipes.

Undulating Rim Platter, 16 inches in diameter, wheel-thrown and altered white stoneware, with Blue-Green/Copper Red Glaze sprayed over scrap glaze, fired to Cone 6 in reduction.

by Rick Malmgren

Traditional Cone 10 Glazes Make the Leap to Cone 6


Blue-Green/Copper Red Glaze

Cone 6, oxidation or reduction Talc . . . . . . . . . . . . . . . . . . . . . . . 3 .30 %Whiting . . . . . . . . . . . . . . . . . . . . 14 .29Frit 3134 (Ferro) . . . . . . . . . . . . . . 13 .33Kona F-4 Feldspar . . . . . . . . . . . . 46 .16Edgar Plastic Kaolin . . . . . . . . . . . 6 .40Flint . . . . . . . . . . . . . . . . . . . . . . . 16 .5%.2 100 .00 %

Add: Tin Oxide . . . . . . . . . . . . . . . 2 .24 % Zinc Oxide . . . . . . . . . . . . . . 4 .37 % Black Copper Oxide . . . . . . . 1 .07 %A lovely celadon blue-green in oxidation . In reduction, bright red; the color tends to burn off when near a heat source . Covering with clear glaze helps reduce burning out of the red .

Shino Glaze Cone 6, reduction

Soda Ash . . . . . . . . . . . . . . . . . . . . . . 10 %Spodumene . . . . . . . . . . . . . . . . . . . . 40Nepheline Syenite . . . . . . . . . . . . . . . 40Edgar Plastic Kaolin . . . . . . . . . . . . . . 10 100 %

Apply very thinly to give an almost salt-glazed look in reduction . Tends to be a bit bland in oxidation, but an addition of 4% rutile seems to warm it up a bit .

Temmoku GlazeCone 6, reduction

Whiting . . . . . . . . . . . . . . . . . . . . . . . 20 %Custer Feldspar . . . . . . . . . . . . . . . . . 35%.Kentucky Ball Clay (OM 4) . . . . . . . . . 15%.Flint . . . . . . . . . . . . . . . . . . . . . . . . . . 30 100 %

Add: Red Iron Oxide . . . . . . . . . . . . . . 10 %A Cone 10 recipe that works equally well at Cone 6; yields yellow “tea dust” crystals in reduction . Not as interesting in oxidation; just lies there and looks brown .

Straw GlazeCone 6, oxidation or reduction

Dolomite . . . . . . . . . . . . . . . . . . . . 13 .1 %Lithium Carbonate . . . . . . . . . . . . . 3 .3Whiting . . . . . . . . . . . . . . . . . . . . . 3 .9Frit 3134 (Ferro) . . . . . . . . . . . . . . . 27 .5%.Edgar Plastic Kaolin . . . . . . . . . . . . 22 .2Flint . . . . . . . . . . . . . . . . . . . . . . . . 30 .0 100 .0 %

Add: Copper Carbonate . . . . . . . . . 2 .5%. % Red Iron Oxide . . . . . . . . . . . . 2 .0 %A mossy green glaze (in oxidation or reduc-tion) with matt crystals suspended within glassy fields . Very promising when tested with other colorants, including white (add-ing no colorants) and blue (adding 1 .5%.% cobalt carbonate) .

SDSu Texture/Crawl GlazeCone 6, oxidation or reduction

Magnesium Carbonate . . . . . . . . . . . . 25%. %Nepheline Syenite . . . . . . . . . . . . . . . 70Kentucky Ball Clay (OM 4) . . . . . . . . . 5%. 100 %

Richard Burkett posted this glaze on Clayart several years ago . It is very sensitive to thickness . Use by itself or over a contrasting glaze . Colorants can be added .

Marilee’s Lava GlazeCone 6, oxidation or reduction

Whiting . . . . . . . . . . . . . . . . . . . . 23 .91 %Custer Feldspar . . . . . . . . . . . . . . 49 .73Edgar Plastic Kaolin . . . . . . . . . . . 13 .18Flint . . . . . . . . . . . . . . . . . . . . . . . 13 .18 100 .00 %

Add: Titanium Dioxide . . . . . . . . . 11 .29 % Silicon Carbide . . . . . . . . . . . 0 .34 %A very rough glaze; not intended for food surfaces . Fine silicon carbide seems to work best . For a gray-to-black variation, add 7% Mason stain 6600 .

SJC Turquoise/Red GlazeCone 6, oxidation or reduction

Gerstley Borate . . . . . . . . . . . . . . . 5%. .1 %Whiting . . . . . . . . . . . . . . . . . . . . . 5%. .8Custer Feldspar . . . . . . . . . . . . . . . 34 .9Frit P-25%. (Pemco) . . . . . . . . . . . . . . 25%. .3Kentucky Ball Clay (OM 4) . . . . . . . 3 .6Flint . . . . . . . . . . . . . . . . . . . . . . . . 25%. .3 100 .0 %

Add: Copper Carbonate . . . . . . . . . 3 .0 %A glassy green in oxidation; in reduction, a bright red . Good when used to overlap other glazes . When sprayed over Annette’s Florida Tan, it gives a highly speckled look, particularly where it is thin . The two base glazes can be colored with different color-ing oxides and still give the same speckled look when they overlap .

Annette’s Florida Tan GlazeCone 6, oxidation or reduction

Dolomite . . . . . . . . . . . . . . . . . . . 6 .5%.8 %Gerstley Borate . . . . . . . . . . . . . . 13 .05%.Soda Ash . . . . . . . . . . . . . . . . . . . 0 .11Talc . . . . . . . . . . . . . . . . . . . . . . . 13 .05%.Custer Feldspar . . . . . . . . . . . . . . 41 .01Edgar Plastic Kaolin . . . . . . . . . . . 6 .5%.8Flint . . . . . . . . . . . . . . . . . . . . . . . 19 .62 100 .00 %

Add: Zircopax . . . . . . . . . . . . . . . 9 .65%. % Red Iron Oxide . . . . . . . . . . . 1 .97 % Rutile . . . . . . . . . . . . . . . . . . 5%. .48 %Best as a background for other glazes, such as SJC Turquoise/Red . Yields similar results in oxidation or reduction .

Turquoise GlazeCone 6, oxidation or reduction

Talc . . . . . . . . . . . . . . . . . . . . . . . . 11 .7 %Whiting . . . . . . . . . . . . . . . . . . . . . 11 .1Custer Feldspar . . . . . . . . . . . . . . . 14 .9Frit 3134 (Ferro) . . . . . . . . . . . . . . . 23 .4Edgar Plastic Kaolin . . . . . . . . . . . . 19 .1Flint . . . . . . . . . . . . . . . . . . . . . . . . 19 .8 100 .0 %

Add: Cobalt Oxide . . . . . . . . . . . . . 0 .5%. % Chrome Oxide . . . . . . . . . . . 0 .5%. %A lovely magnesium matt glaze that works well in oxidation or reduction; the base glaze also works well with other colorants .

Bronze Green Matt GlazeCone 6, oxidation or reduction

Whiting . . . . . . . . . . . . . . . . . . . . 24 .20 %Custer Feldspar . . . . . . . . . . . . . . 5%.4 .90Edgar Plastic Kaolin . . . . . . . . . . . 14 .30Flint . . . . . . . . . . . . . . . . . . . . . . . 6 .60 100 .00 %

Add: Zinc Oxide . . . . . . . . . . . . . . 9 .90 % Cobalt Oxide . . . . . . . . . . . . 0 .44 % Copper Carbonate . . . . . . . . 2 .97 % Rutile . . . . . . . . . . . . . . . . . . 5%. .94 %

Rust Red GlazeCone 6, reduction

Bone Ash . . . . . . . . . . . . . . . . . . . . 4 .0 %Talc . . . . . . . . . . . . . . . . . . . . . . . . 4 .0Whiting . . . . . . . . . . . . . . . . . . . . . 20 .0Custer Feldspar . . . . . . . . . . . . . . . 5%.0 .0Frit 3110 (Ferro) . . . . . . . . . . . . . . . 4 .0Edgar Plastic Kaolin . . . . . . . . . . . . 18 .0 100 .0 %

Add: Tin Oxide . . . . . . . . . . . . . . . . 4 .0 % Black Iron Oxide . . . . . . . . . . . 5%. .0 %A Cone 6 version of Shaner’s Red; it is very sensitive to application thickness, reduction and clay body . The best reds seem to come from relatively thin applications on high-iron clays, with a moderate reduction from Cone 010 to the end of the firing .

Angle Cut-Rim Vase, 11 inches in height, with SJC Turquoise sprayed over Annette’s Florida Tan Glaze, $90, by Rick Malmgren, Lo-thian, Maryland.

cone 10 cone 6

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