I am still searching for Stable glazes that have colors I like. I look for 3 Things in a glaze before I ever test it or buy chemicals for it.
- SiO2 is the Silica level in a glaze and the first thing to look for when searching for stable glazes. 2.5 or above with (3.O-4.O is ideal). Above 4.O is harder to melt in a glaze.
- Alumina Level Al2O3 is the second thing I look for. 0.25-.5 Is the range I am using ( higher than .45 might be harder to melt in a glaze).
- Ratio of Silica to Alumina Si : Al
- In a glossy glaze above 8
- In a matt is 5 or less
A side note on Matts, you can get them in between ratios but they might not be melted matts. You can have a matt that is 8 or higher but it wasn’t melted all the way and not good for functional work.
I fire to cone ^6 Oxidation with a slow cool and work towards those ratios in my glazes.
Cranberry Cone 6 Glaze has a Silica level of 3.016 which is in my GOODRange. Rasberry has a Silica level is 2.707 Still ok . Jeannie’s Purple is SiO2 is 3.016 my GOOD range.
The Ratios between Silica and Alumina in all three glazes are above 8 which means they are glossy or semi-glossy cone 6 glazes.
2 responses so far ↓
Linda Starr // June 10, 2009 at 8:40 AM |
Mary, this is some really good information, thanks so much. I like the color above. Can you not have two different ones; maybe a half a batch of each. I now lots of folks like a lighter color and this one fills the bill, but brick red can be so nice too.
Mary Starosta // June 10, 2009 at 11:56 AM |
Ahhhh I think you are “right on” I really love the color that out of the fire got recently. They use a brown clay as well where I think John Post might use white stoneware,etc. i will let you know if I can come close to a brick red!