Sunday, April 28, 2013

Always testing

Here are the two successful tests.

The first is a cone 6 snowflake crackle from John Britt/ Hard to see it in this phone camera pic but it really does have a nice crackle. I didn't get the snowflake effect but I suspect it wasn't thick enough.

This one is a cone 6 oil spot with a cover glaze, again both are from John Britt. This turned out great. I just used 11% zircopax as a colorant. I have test batches mixed with crimson stain and copper carbonate. 

Speaking of tests... this was my morning. All are different base glazes or existing glazes I have used in the past. I want to get a baseline set of tests then start tweaking from there. There are 4 different iron reds in that picture. A number of ash glazes and some strontium matte glazes. 

Thursday, April 25, 2013

Starting over

Glazes don't travel. It's a truism for ceramics. Ingredients are different, kilns are different, clay bodies are different. There are just too many variables to accurately reproduce a glaze someone else developed.

I had developed a small palette of glazes that worked well with my chosen clay, in the studio I worked in. I was content. Then I took a long break. I started back into ceramics. It was getting back on a bike. I had no difficulty throwing again. In fact somehow during the break my throwing improved. I now throw noticeably better. No idea why or how.

What I forgot was that glazes don't travel. I threw about 12 nice bowls. I glazed them using glazes I had used for a long time with success; an iron red, a black, a cone 6 ash glaze. I have used all with no issues many times. But I was firing in a new kiln. All 12 bowls were ruined. The glazes came out horrific. The iron red came out a very nasty tan, the surface completely matte due to iron crystals. The black glaze, same thing. Completely matte due to crystals. The ash glaze had been very well behaved at cone 6. Nice webbing but not too much running. It ran everywhere and ruined several shelves.

By looking at the  results I got I assumed this new kiln cooled much slower than I am used to. Indeed I found that the kiln is programmed to cool very slowly just in case there are platters. Seems they had an issue with platters cracking in the past so now they cool super slow.

While it means that I ruined some bowls it's also a great situation to be in. I am firing in a new kiln that cools really slowly. Time for more glaze tests to get glazes stable in this new firing cycle. I am hoping to use some crystalline glazes.

I haven't posted pics of my first two glaze tests in the new kiln, a crackle and a cone 6 oil spot. Both came out great. The crackle is completely unaffected by the slow cool and the oil spot is improved by it. Pictures will be posted next week. Really.