Folks who have visited me at a booth or Open Studios know that I make my own glazes. I find commercial glazes to be both inferior and exhorbitantly expensive, and I learned pottery back when they simply weren't available. So it's all glazes I formulate, or mix based on others' recipes.
All of this means doing lots and lots of glaze tests in order to get a small palette of good glazes: on the order of 30 to 40 tests per keeper glaze. I generally put a few glaze tests into every glaze firing I do. What follows are the tests for this month.
First things first: our Toki Kiln is overfiring. For some reason the folks in Berkeley think that cone 6 is 2232F, which is about 30F over what I'd put it at, especially on a 13 hour firing, and the cones agree with me. So this was a Cone 7 glaze test.
Let's start with the big success. This is Orange Street, a glaze which has been sweeping the folks on the Ceramic Recipes Facebook Group because it is so awesome. The blog title picture is Orange Street on a test cup. It's more red than it was for other folks who have used the recipe; that could be because of the overfiring, or it could be differences in the materials, especially Talc.
Interestingly, the test with 15% Red Iron Oxide looks pretty much indistinguishable from the test with 18%. While iron is cheap enough I don't care, it would be worth reducing the iron in order to reduce leaching.
- Silica 13%
- Talc 11.5%
- Dolomite 7%
- EPK 4%
- Gerstley Borate 15%
- Minspar 39.5%
- Bone Ash (Tri-calcium phosphate) 10%
- Red Iron Oxide 15% to 18%
Randy's/Toby's Red (this glaze has had a lot of names), though it has the same chemicals in slightly different proportions, didn't do nearly as well. As you can see it's mostly black; this could be due to materials, or to the overfiring, or something else. I've been told that if I refire it to bisque temperatures more of the red will come out; I'll try that, but with Orange Street looking so similar and already working, I'm not sure it's worth troubleshooting this glaze.
Far less successful was my attempt to create a chrome green, so that I would have a deep forest green in a glossy translucent glaze. I tried adding Chrome in different concentrations to the two Glossy Bases from Mastering Cone 6 Glazes, but ended up getting a semi-matt glaze out of it; somehow the chrome changes the glaze so that it doesn't get glossy. Will have to start over with a different base, or maybe try the reformulated bases from the website (due to materials changes).
More tests on this blog tommorrow ...