Wednesday, June 25, 2008

Developing a Fake Ash base glaze

I love Steven Hill's pots. Specifically I love his glazes. His fake ash is delicious. I aspire to have glazes as wonderful as his on my pots. I don't want to simply cut and paste other people's work though. I want my glazes to be my own.

There's nothing new in pottery. Pottery has been around literally as long as man. Virtually nothing I will do hasn't been done before.

These two opposing paradigms are what we all need to balace in developing our own glazes; something wondeful and new yet you can bet your ass someone has done it first. Even if you don't copy someone else you're probably not the first one to do whatever it is you're doing. Such is the world of potting.

I am working on finding a base fake ash glase. I am looking for a fake ash glaze that works well on both stoneware and porcelain at cone 6 in an oxidizing electric kiln. Further I want a fake ash glaze that takes color. I have visions of a red fake ash... or a purple. In order to do this I need to find something that will color a glaze overloaded with calcium red or purple. Off hand I don't know what I need to do.

I am starting with two base recipes.

Via Ceramics Monthly Satori Yamaoka's synthetic ash:

Magnesium Carbonate ........................ 6%
Phosphorus Pentoxide ........................ 6
Whiting .................................................. 63
Potash Feldspar ................................... 12
Kaolin .................................................... 10
Silica (Flint) .......................................... 3

I am swapping out the Phosphorus Pentoxide with Bone Ash.

Magnesium Carbonate ........................ 6%
Bone Ash ............................................... 6
Whiting .................................................. 63
Potash Feldspar ................................... 12
Kaolin .................................................... 10
Silica (Flint) .......................................... 3

This recipe is originally listed as cone 9. I am working at cone 6. In order to get this to melt properly need to drop the melting point. As a starting point I am going to swap the Potash Feldspar with Neph Syn.

Magnesium Carbonate ........................ 6%
Bone Ash ............................................... 6
Whiting .................................................. 63
Nepheline Syenite ............................... 12
Kaolin .................................................... 10
Silica (Flint) .......................................... 3

The resulting analysis:

Unity Oxide
.025 Na2O
.008 K2O
.099 MgO
.868 CaO
1.000 Total

One thing about this one I notice long before I put on the mask and mix it is that it does have what I would expect as the high enough percentage of CaO to be a good fake ash glaze. I am not sure if this will melt and flow at cone 6. If not my next step will be to add some lithium and possibly increasing the amount of bone ash.

Next since I have a man crush on Steven Hill's glazes I am starting with his fake ash glaze via John Britt's aswesomesauce book "The Complete Guide To High Fire Glazes"

Feldspar--Kona F4 ... 6.8
Dolomite ..................... 3.8
Whiting ....................... 45.5
Kaolin--EPK ............... 30.3
Silica ............................ 13.6

Total ........................... 100

Bentonite ................... 2.3

Like the Yamaoka's glaze this was designed for high fire and I am working at cone 6 so I need to drop the melting point. I am less sure of this conversion and will probably have to try several iterations of this. First lets trade the Feldspar for F3134.

F3134 ......................... 6.8
Dolomite ..................... 3.8
Whiting ....................... 45.5
Kaolin--EPK ............... 30.3
Silica ............................ 13.6

Total ........................... 100

Bentonite ................... 2.3

I don't think this will be enough to drop this to cone 6 runny goodness. I am going to add some lithium, 3%.


F3134 ......................... 6.8
Dolomite ..................... 3.8
Whiting ....................... 45.5
Kaolin--EPK ............... 30.3
Silica ............................ 13.6
Lithium Carbonate .... 3

Total ........................... 103

Bentonite ................... 2.3


Unity Oxide
.072 Li2O
.006 Na2O
.002 K2O
.042 MgO
.878 CaO
1.000 Total

I will normalize this to total 100 again if this works. Otherwise I am not wasting my time. Not that the math is hard, it just a waste of time if this isn't the final version. I only want to do it once.

So those are the recipes I am going to test. I'll add some cobalt to each batch because I tried testing a fake ash glaze one with no coloring agent. It's a challenge.

3 comments:

geolewter said...

If you join cone6pots.ning.com, You will find that Steven Hill is a prominent member. I attended his Sept 4-7 workshop and have the recipe for the current fake ash glaze he is using. We have an interest group "The Steven Hill Oxidation Project" one of the aims of which is to get his effects at Cone 6. This group is just starting and the goals are not yet fully developed, but it is primarily for his students to keep in touch, keep progressing, and to work on some of the challenges in a cooperative manner. Give us a look.

entropicalbliss said...

Trinity ceramics in Dallas has excellent red stain that holds at cone 6 and I know for a fact manganese carbonate will purple your base, if you can find it.

Eric Preece said...

Thanks for the tip on the manganese carb. I am ordering some and will do a line test to see what I can get. Also I am going to check out Trinity ceramics. If they have a red that holds up at cone 6 they might have other colors as well.