... continued from part 1

One glaze I used to have when I fired cone 10 electric which I really miss was one I called Verdigris. It was based on a Val Cushing Cornwall stone matt glaze recipe, with tin and copper so that the glaze was actually bronze:

I've been trying for a few years to "down-temperature" this glaze without success. Recently someone recommended a Cone 6 recipe called Pinnell's Matte, which is widely popular. The recipe I was given used copper and titanium, which didn't work out so well, but based on experience I also tested copper and tin. This is a lot more promising:

Please note that the picture is mislabeled; it should be Tin/Copper, not Copper/Tin. The tile on the right is 8% copper, not 8% tin.

I need to flocculate the glaze (it's 60% Nepheline Synenite), so that it will go on thicker and stay suspended, and test further. But that's promising.

Pinnell's Matte Bronzed?

• Nepheline Syenite 60%
• Ball Clay 8%
• Bentonite 2%
• Strontium Carbonate 20%
• Flint 9%
• Lithium Carbonate 1%
• Copper Carbonate 5%
• Tin Oxide 5%

The other glazes I've been trying to reproduce at Cone 6 are a set of glazes made with raw wood ash from my in-laws' fireplace and furnace. This is a mixture of madrone, pine and cedar ash. I'm looking to produce both a clear yellowish glossy glaze with impurities which looks like the piece came from a wood firing, and a second runny glaze which I can color and put at the tops of pieces for interesting effects. I got some promising leads on both.

My big trial was a simple ash glaze recipe made with RedArt clay. I got this idea from one of the potters at the annual ClayFolk show, who has some quite nice ash glazes based on it.

As you can see, this ranges from a shino-like satin glaze all the way to a glossy slightly runny glaze.

The 30% or 40% would be good candidates to replace my "fake wood firing" ash glaze; I'll test further.

RedArt Raw Ash Glaze No. 1

• RedArt Clay 40%
• Ferro Frit 3124 10%
• Raw Wood Ash 30% to 60%

I also did a test of a slightly different glaze based on a recipe from Ceramic Recipes group. This recipe uses a much higher percentage of Ferro Frit 3124, and much less ash. I wasn't impressed.

There are a lot of old recipes on the internet and in old books which use raw wood ash and Albany Slip as a glaze. While Albany Slip is long gone, Laguna mines a California clay known as Arroyo Slip. You'll notice the middle tile stuck to one of the other test tiles; such are the perils of testing glazes. This produced a much more promising result for a runny ash glaze; it bunched and dripped like I want. You can see this more on the backs of the tiles:

Based just on this test I'd say the 40% is promising, except that I know the kiln was overfired, so maybe I should go with 45% instead. The 2% Cobalt is also a bit dark, and I'm wondering about using 1% instead.

Arroyo Slip Raw Ash Glaze

• Arroyo Slip 40%
• Ferro Frit 3134 10%
• Raw Wood Ash 40% to 50%

Anyway, a mere three dozen test tiles (including some failures I didn't show), one good glaze and four worth further testing. That's an exceptional return for a glaze testing batch; usually it's more like one good tile out of all 36. I'm excited to get glazing in 2015.

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.

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/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 ...