glaze tests Dec. 2014, part 2


... 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:

verdigris on pitcher

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:

Pinnell's Matte with copper and tin

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.

redart ash glaze no. 1 trial

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.

redart ash glaze no.1 30%

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%

redart ash glaze no. 2

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.

arroyo slip ash glaze with cobalt

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:

arroyo slip ash glaze running

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.