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cone 5-6 glaze

updated fri 23 apr 99


Earl Brunner on tue 20 apr 99

We have a glaze in the Art Center where I work part time. The five
gallon bucket has lasted three years. Now that is all but gone,
everyone has decided that they particularly like this glaze in
combination with a couple of other glazes. Unfortunately, the previous
lab technician did not leave a formula. It has the nice generic name of
"Purple". Being male, I know red, orange, yellow, green, blue, purple,
brown and black. I'm told that this is a "lavender" kind of purple.
Whatever. I do not have a clue how to make this color. We fire to cone
5-6 oxidation. Well, actually I might have a little clue, I found some
"Pansy Purple" Mason stain in one of the cupboards. I hate the thought
of mixing up a five gallon bucket of glaze using mason stain as a
colorant. This one is around $15.00 per lb. The book says it's only
good to 2300 F. I'm a little reluctant to spend that kind of money.
Is there another way to get this color? Any ideas?
Earl Brunner

Paul Lewing on thu 22 apr 99

You can get a pretty strong lavender color from about 1% or 2% cobalt
carbonate if you use a base glaze that has lots of magnesia. I'm
talking about maybe .40 molecular equivalents of magnesia, and you don't
want a lot of boron, or KNa. Those will make it more blue. And it will
almost undoubtedly be matt, with not much visual texture. If you can't
find a glaze like that, let me know and I'll send you a recipe for one
I'm working on. I'm not sure it's exactly like I'll eventually want it,
but is lavender. Also be aware that, for whatever it's worth, .40 moles
of Mg is way outside the limit formulas for Mg, but you won't get that
color with any glaze that has Mg within the limits.
Paul Lewing, Seattle