glaze tests Dec. 2014, part 1


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.

cone 7 down

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.

orange street 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.

Red-Orange Street

  • 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 Red or Toby's Red

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.

MC6G GB1 with chrome

MC6G GB2 with chrome

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 ...