Northern Clay Center gallery artist Matt Kelleher used to soda fire stoneware to cone 10, but recently sent in a shipment of cone 3 soda-fired earthenware. I spoke to him about this technical change and the challenges and benefits it has presented so far.
NCC: What was the impetus for you to go from cone 10 stoneware to cone 3 earthenware?
MK: I wanted to change the background of the pots. I started layering high-iron slip on stoneware before my flashing slip and it dawned on me, I could use a higher-fire earthenware body instead.
NCC: How did you know which cone to go to?
MK: Good Question. I know back in the 50’s and 60’s cone 3 was considered “mid range” and people were getting bright colors, but they were also mostly using lead glazes. High-iron clay at stoneware temperatures, especially when it is reduced, can cause a lot of problems. At cone 04 the clay is still so porous, so I thought, how far can I stretch an earthenware body?
If I had to move to cone 1 or cone 4, I would be fine with that, but cone 3 is where I started. It has been about 5 months since I started this quest, and I am not entirely happy. I struggle finding slips that work. Most glazes cloud or bubble. The majority of my testing has been in an electric kiln and then when you put them in the soda firing, they tend to freak out and wrinkle or bubble.
Images: Top row, Pitcher and close up, an example of Kelleher's surface at cone 10. Bottom row, Tumbler and close up, an example of Kelleher's surface at cone 3.
NCC: Do you still reduce at cone 3?
MK: Yes, by reducing I am able to create more flash, but have to balance that with a higher tendency to bloat. The reduction will cause the iron in the clay to flux and this melt ultimately makes it weaker. So I am going for a mild reduction to try to reduce the surface flashing slips.
NCC: Have you used a specific book or reference person to help you through this process?
MK: No, I took a lot of clay and glaze chemistry classes in school, so I am trying to work through this with triaxial blends and get to know the materials again myself. I started with materials I know work at cone 10, hoping that I could still use them at cone 3. But, feldspars have not worked—I have had to use frits, which are weird to me.
NCC: Have you had any aha moments or big disappointments?
MK: My biggest disappointment has been that Gillespie Borate hates reduction and soda—it wants to bubble. Also, Kaolins (Tile 6, Grolleg, EPK) except for Helmer Kaolin, all tend to go grey. Goldart has worked great. I have needed to use a much “dirtier” material to get flashing whereas at cone 10, I almost exclusively used Tile 6. So, I wonder what is happening in that 200 degrees that flashes Tile 6?
NCC: Are you using your same kiln?
MK: I actually built a kiln out of gathered materials. I wanted to use soft brick; hard brick is where so much of the gas expense comes from. The kiln I have now is about half soft brick, half hard brick. I did put a commercially made high refractory coating from Larkin on the soft brick and--I have only done about 10 firings--but it is holding up fine. I thought I would cut my gas cost in half by using soft brick and it has been more like a cut by 60%. However, gas prices are going up so much, I am not seeing as much savings. And they will only get higher.
NCC: Any other thoughts you would like to share about this transition?
MK: Nothing I am doing now is set in stone—this is a curiosity I am exploring. By doing this, I’ve heard of others working at cone 3. I know Alfred is teaching a variety of mid range possibilities, which is exciting. It comes down to formulating the materials at the temperature you want in order to get the results you seek. I am encouraged by the conversations I have had with others exploring different mid range temperatures. People seem to be getting in better touch with materials.
This interview was inspired by the fact that Northern Clay Center just worked with Donovan Palmquist to re-build its 12 year-old soda kiln. While he was here building the new kiln, we talked about mid range soda firing, and Donovan recommended a 1982 Ceramics Monthly article on Neil Tetkowski. It is written by Janet Kopolos and shows some of his gorgeous salt fired earthenware work.
NCC offers a Soda Firing class twice a year; between students, studio artists, and staff, the soda kiln usually gets fired two to three times a month. There are quite a few people in the Northern Clay Center Gallery who soda fire: Matt Kelleher, Leila Denecke, Bill Gossman, Lee Love, Josh DeWeese (a combination of wood, soda, and salt), and Jeff Oestreich (salt/soda fired in oxidation).
Please feel free to email me with any comments or questions about this interview. Thanks for your interest! - Karen