A High-Fire Reduction Potter Develops Great Glaze Recipes for Oxidation Firing to Cone 6 in Electric Kilns

“Alligator Plate,” 12 inches (30 centimeters), stoneware, with Matt Black, Costello Carbonate and Alligator Green glazes,.

“Alligator Plate,” 12 inches (30 centimeters), stoneware, with Matt Black, Costello Carbonate and Alligator Green glazes,.

With an initial impetus in the energy crisis of the 1970s, Jayne Shatz began exploring options for translating her high-fire reduction glazes into cone 6 oxidation glazes for electric kiln firing. While the exact results were not possible, she learned a lot about glazes and came up with some nice results.

 

In today’s post, an excerpt from the second edition of our free download Techniques and Tips for Electric Kilns: Inspiration, Instruction and Glaze Recipes for Electric Kiln Firing, Jayne passes those recipes on to you. – Jennifer Harnetty, editor.

 


 

In 1976, I was forced to “go electric” when a cooperative studio I was a member of closed because of the energy crisis. At that time, my contemporaries looked down on electric kilns and oxidation glazes. After all, we were hurly-burly, brick-and-burner, reduction-?red gas guzzlers! But all that was changing. I had to make my way in a strange new world.

 


For more of Jayne Shatz’s Cone 6 oxidation glaze recipes, be sure to download your free copy of
Techniques and Tips for Electric Kilns: Inspiration, Instruction and Glaze Recipes for Electric Kiln Firing.

 

 

“Pedestal Bowl,” 12 inches (30 centimeters) in height, stoneware, Glossy Black over Blue Matt glaze.

Having built three large outdoor brick kilns, I felt I was committing a despicable act by purchasing an electric kiln. It was stainless steel, shiny and fit into a corner of my basement studio. I had no clay bodies, glazes or low-temperature experience. I bought this kiln because it had the potential of ?ring up to Cone 10. But I soon asked myself, “Why bother ?ring up to Cone 10 when Cone 6 would be more cost effective?” After all, it wasn’t the temperature range that was so cataclysmic; it was the fact that I was switching over from reduction to oxidation. That was the whole ballgame. Ultimately, I committed to working at Cone 6 in oxidation, and recreating the glazes I was accustomed to using at Cone 10 in reduction.

 

I surveyed this problem in its most rudimentary components. Simply speaking, a reduction clay body develops its toasty warm color when the oxygen entering the kiln is reduced by closing down the kiln’s dampers. This reduction of oxygen and increase in carbon creates the autumnal colors of reduction stoneware.

 

Click to enlarge!

I read everything I could on clay bodies and clay chemistry. I finally developed a Cone 6 clay body that was rich in iron and would develop into a toasty warm color in oxidation.

 

Painstakingly, I developed a white porcelain clay body with which I was satis?ed. It was not translucent, but that was not a quality I was pursuing. Because of this characteristic, and the midrange temperature, there is some debate over whether or not it is truly porcelain. For me, it is a clay body that is beautifully white, dense, nonbrittle and throws fantastically. The body contains bentonite, enabling it to be plastic and very strong. It even can be once fired. I found out years after I developed the body that my clay distributor believed it to be one of the best slip-casting bodies he had ever used. It is now used by several tile and slip-casting companies for industry. I can be very casual with it, due to its plasticity and strength, and it is fabulous for large sculptural pieces. With the addition of sand, it becomes an excellent white raku body.

 

Then I began bringing down the melting temperatures of my glazes to Cone 6. I delved further into chemistry, learning the various effects oxides produced in an oxidizing atmosphere. Very slowly, and with many glaze tests, I began to obtain the colors I was seeking. My ?rst success was to duplicate an iron saturated glaze from my college days, Ketchup Red [see recipe]. I then continued down my palette of glazes. This process took two years. I continued selling pottery during this time, which meant that, for a long time, I was working with only one glaze. Fortunately, people were buying my pots.

 

Click to enlarge!

After much work, I produced a wonderful clear glaze for my porcelain. It was very clean on the surface and pooled into crevices, where it transformed into a lovely robin’s egg blue. It reminded me of the beautiful “Scarab Vase” by Adelaide Alsop Robineau. If you look closely at that pot, the pooled areas are a lovely soft blue. This realization hit me like a thunderbolt! What I should have done so many years ago was research the glazes of American Art Pottery. Ironically, many of those potteries worked in oxidation. The answers were there; I just didn’t know where to look.

 

I discovered that, by layering glazes, I could achieve certain Cone 10 reduction effects. I learned to work with base glazes, varying the oxides to make additional glazes.

 

The years progressed and it seemed the entire country was firing electric. Kilns got better, clay and glaze recipes filled books and publications, and the Internet was born. Oxidation firing in American ceramics flourished—and here we are.

 

For further information on the work of Jayne Shatz, see www.jayneshatzpottery.com.

 


For the rest of Jayne Shatz’s Cone 6 oxidation glaze recipes, be sure to download your free copy of
Techniques and Tips for Electric Kilns: Inspiration, Instruction and Glaze Recipes for Electric Kiln Firing.

 

Comments
  • I realize I should know this but I don’t. Several Cone 6 recipes in today’s posting of Techniques and Tips for Electric Kilns call for barium carbonate. I prefer to substitute the functional food container safer strontium carbonate but don’t know
    1. What the ratio of barium carbonate to strontium carbonate is
    2. Whether the authors or anyone else has tried the substitution and what the results yield.
    Thanks.
    Marcia

  • Marcia,

    You might check out the “Leaving Bariumville” article. It may have some helpful info on that substitution.

    /ceramic-glaze-recipes/glaze-chemistry-ceramic-glaze-recipes-2/leaving-bariumville-replacing-barium-carbonate-in-cone-10-glazes/

    -e

  • Surely she does not mean 86.9 of zircopax in the aligator glaze? Very nice article. Thank you.

  • Same comment as Rosemary – 86.9 Zircopax??????

  • Hello all-

    When this article was originally published we received a lot of emails about the zircopax content. That is indeed the amount Jayne uses in this glaze. Here is a quote from her in response:

    “It is very volatile and reactive [because of the zircopax]. It sputters, crawls, fissures, sometimes even shoots off the pot during firing. Use it with caution. I usually use it on flat forms. I love it for its unusual and disruptive appearance on vessels as well as sculptural forms, though it shouldn’t be used on [surfaces that will come in contact with food.]”

    Hope that clears things up!
    Jennifer Harnetty, editor.

  • I got all excited about the alligator green glaze. Should have known that was too good to be true.

  • Our cone 6 fires at about 2220 F so 1215C. 1540C is way above cone 10!

  • My comment is going to sound so lame in comparison to these others but here goes anyway. Years ago, everything was written about and for reduction firing with cone 10 being the chief cone temp. I fired at cone 6 oxidation in and electric kiln..I still do but what I see now is that cone 6 is everywhere…it took a long time coming..but it is a popular firing temp these days…I have a lot of great recipes for cone 6 that my teacher gave me. I have these today..I dont have a sample picture of them but there is a great green matt glaze, I think I will dig out them recipe book and print that recipe here…give me a couple of days to get it together…

  • I agree with Valerie, but I believe the difference is…. the big cone 6 swing these days is to try to mimic Cone 10 reduction in a lower temp oxidation environment. In the past it was just cone 6 oxidation for the sake of Cone 6 oxidation. It is obviously much easier to program an electric kiln and leave it until its cool, versus firing a gas kilns for 7 ++ straight hours.
    In college we had two options Cone 10 Reduction or Cone 6 oxidation. I stuck with Cone 10 Reduction

  • I have used the ketchup red a lot.It is one of my favorite glazes.I found out that if you are teaching a bunch of students,that some of them will do your glaze testing for you .you just have to hope they can remember what they had done.As for the red,putting it on real thin works best,credit due to one of my students.

  • Sorry 😉 I was up late yesterday ( Norway is 6 hours ahead of New York ) I burn my works at 1250C – not 1540C I lied about. So I guess thats cone 7 or 8?

  • I though copper and barium couldn’t go together on a pot used for food due to leaching, is that right?

  • I have never heard of either copper OR zirconium being subject to leaching into food, nor of any toxicity from either element in a fired glaze. Of course many of the materials we use are hazardous in particulate form, even clay itself.

    The problems of toxicity occur when foods or beverages of a HIGH acidity come in contact with lead compounds or barium in fired glazes. Acid foods, like tomato or citrus, vinegar in salads….things like that. And remember, this has to be CHRONIC exposure, repeated over time, before you’ll see ill effects. Prudence is one thing, paranoia quite another. Chemophobia is a disease too.

  • Copper should be used sparingly if at all in a liner glaze or not at all. Coffee for instance is a mild acid and will leach copper out of a copper glaze. I’ve found this to be the case in most copper glazes, especially ones like Rob’s Green which has about 2% copper. Even tea will pull enough copper out of Rob’s Green that if you drank a pot of tea per day it will lead to chronic copper exposure.

    I first addressed this problem in my own work by using a durable liner glaze that has no colorants in it save 1% iron for a creamy color. This is satisfactory in my coffee cups etc, though the high contrast and light color of my liner makes my glazing sort of two dimensional.

    I believe a liner glaze is in order in most functional ware. My mentor and long time friend uses a Tenmoku glaze as his liner because of the low chance of leaching iron. Tenmoku’s lower contrast with his copper green/blue matte makes his work more dynamic and professional. Tenmoku also breaks giving each pot it’s own distinct characteristics inside and out.

  • Here’s a few links for cone temperature charts. The temperature vary according to the increasing temperature rate, degrees per hour.

    http://www.keithcompany.com/clientfiles/Cone%20chart.pdf

    http://www.keithcompany.com/clientfiles/Cone%20chart.pdf ( I had never heared of the warning on that one, glad to have found it)

    http://www.miniworlddolls.com/evenheat/ConeInfo.htm

    I’ve been working on cone 6 glazes but not cone 10 to cone 6 translation. Here come a new challenge!

  • I need some cone 6 matt glaze receipes that work on standard #365. Are there any out there?

  • I’m electric—have been since 1960. Classes in ceramics in night school was the only firing heat we had, so we dealt with it ! You learn what yoou can do with it !!!!

  • I cant comprehend the effort to reformulate those glazes but not get rid of the Barium. Barium, Lithium, Lead…there is no reason to use these materials anymore. You might as well lace them into a Jeffery and smoke it.

  • can someone give me a recipe for cone 6 glossy metalic black with the grams instead of percentages (non math human) would really appreciate thank-u

  • To Pete, Re: “CHRONIC exposure”

    Ceramics are absolutely conduits of repeated exposure. If you drink from your favorite coffee mug once per week (and who would use it so infrequently?), that is certainly repetitive. And beside habitual exposure, our bodies just do not clear all of the compounds they are absorbing. Glazes that contain certain metals (Pb, Ba, etc.) should be avoided reflexively; but according to the chemical reactivity series and simple biochemical roles, or lack thereof, a wider variety of metals are still dangerous and should be avoided. Cu can be one of those; you could even be poisoned by Fe. . . So while it’s pleasant not to be afraid of chemicals, they’re very real actors in our physiological health.

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