Soda Fired Commercial Clays

So I wanted to see what all of my locally available commercial clay looked like in our Soda Kiln. I took 12 commercially available clay bodies tested in this base recipe to get an idea which were more likely to flash:

10 Nepheline Syenite, 10 200m Silica, 80 Clay

For good measure I threw in a few Shino glazes, and tried calcined EPK for the hell of it (I actually wanted to see if it deflocculated like the rest of them.. it didn’t really…)

From the 100g test batches, I then tested each slip/shino on Laguna 550 Porcelain, B-Mix, and Miller 510 Stoneware in 2 firings that were unfortunately pretty similar in atmosphere and soda introduction. First firing on top, 2nd on bottom. Tiles were scattered throughout the kiln, so some got blasted, others not so much.  Standard body reduction and reduction firing to cone 9/10, heavy reduction during soda intro, and reduction cooling from 2300-1800F. I scanned the sides that were more interesting, or showed more variation. Hope this helps you narrow down what you might be looking for with soda fired clay slips!

Cone 10 Greenware Slips (Engobes)

Here’s the newest round of slips for leather hard/stiff application.  All but #7 will work for bone dry application. Not tested (yet) for bisque application.  Fired to cone 10 flat in a hard reduction.  Left side is super thick, right side is thinner.  Clay body is a Hawthorn/Goldart/OM4  stoneware – nothing fancy.

c10 Engobes
C10 Engobe Recipes
C10 Engobe Tiles
C10 Engobe Tiles

#1 Greenware Slip: Grolleg Kaolin 40, OM4 Ball Clay 10, Custer 25, Silica 25
#2 Greenware Slip v.1: EPK 25, Grolleg 25, OM4 Ball Clay 10, Custer 25 Silica 25
#3 Bringle Slip: EPK 20, OM4 20, Neph. Sye. 25, Silica 30
#4 BS v.1: Grolleg 25, OM4 25, Neph. Sye. 25, Silica 25
#5 BS v.2: Grolleg 30, OM4 10, Neph Sye 20, Silica 20
#6 Coleman Clay: EPK 50, Silica 25, Custer 25, Frit 3110 5
#7 CC v.1: Grolleg 50, Silica 25, Custer 25, Frit 3110 5
#8 Porcelain Slip: Grolleg 30, OM4 8, Custer 30, Silica 30, Bentonite 2

Pete's Clear
Glazed C10 Engobes

The light is cheating these a little bit. #1,2, and 8 seem to be the whitest, with not much differentiating them. #1 seems to promote the best celadon blues, although timing is critical, because it cracked when applied to a bone dry tile.  #2 seems to be a perfect middle ground in terms of versatility, cost, and whiteness. In my experience, the difference between a 50/50 grolleg/epk and a 100% grolleg clay body is negligible in cone 10 reduction.  The case could be made that it really matters in oxidation – which is just now bringing to mind the need to test these in c6 oxidation.

My picks? For Whiteness:

#2__Greenware Slip___

EPK 25, Grolleg 25, OM4 10, Custer 25, Silica 25, 45cc Water, 5cc Darvan #7,

For Celadon Blue:

#8__Porcelain Slip___

Grolleg 30, OM4 8, Custer 30, Silica 30, Bentonite 2, 50cc Water, 5cc Darvan #7