Thursday, June 26, 2008


A bit on how I test glazes.

I use extruded rectangular tubes. I hand cut them into roughly 4 inch heights. I put one hole through the test tile - just in case I want to hang it. I have a little seashell that I press into one side.

I always use porcelain for the test tiles. I usually work in porcelain so that helps. I usually want to see the glaze on porcelain. I do some work in a real nice red iron bearing stoneware but I never use it for test tiles. Yeah, I know the clay really impacts the glaze. I have a couple glazes I really like that only look good on the iron bearing stoneware. But also... I am a bit anal and a little lazy. I hate getting the red clay on things that the porcelain uses, like the extruder. If I made stoneware test tiles I'd have to clean the bejeezus out of the extruder and I am too lazy to do that so I just make porcelain test tiles.

I generally make a 300 gram batch when testing a base. I'll mix 300 grams of dry with 200-300 grams of water. I sieve the batch through an 80 mesh sieve twice. Then I dip the test tile in the glaze and fire at cone 6 in one of the electric kilns in the studio I work in.

I usually use witness cones. From using the witness cones the kilns fire about high 5 or low 6. The cone 6 witness cone usually just bends, about 15-20 degrees.

The kilns all have kiln sitters. No computer controlled kilns. Yet. So no soaks. No slow cools.

I have 50+ test tiles drying now. I am going to bisque fire them Saturday morning. So maybe some glaze test firing next weekend.

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