In an effort to extend the life of my elements and save on electricity costs, I have decided to adjust my glazes from cone 8 down to cone 6. Last night I fired each of the 14 studio glazes at cone 6 to see just how much alteration they will need. Several of them are nearly indistinguishable from the cone 8 versions, although not quite as fluid. Some are radically different in color, although not so different in surface quality. And a couple look way under-fired, which does not surprise me at all. Those glazes have always had a very narrow firing range.
This weekend I'll take a look at the recipes and start adding fluxes to bring the melt down to cone 6. Most people say to just add some Gerstley Borate or equivalent frit, but I'm not a big fan of that. Yes, some glazes work that way, but many will not look the same with the addition of Gerstley. Boron, the primary fluxing agent in Gerstley, gives glossy and semi-glossy glazes a certain look. It's almost a little plastic looking in my opinion. I prefer, if possible, to simply increase one of the fluxes already in the glazes. If that happens to be boron, great. Then Gerstley it is. But if there isn't any boron in the glaze, I'll first try something else.
Another note on Gerstley Borate: Don't use it. It's crap, and always has been. I know, that's pretty harsh. But it's true. It's the most inconsistent glaze material available, and for that reason should not be used. But I'll write more on that later. For now I've got to start mixing some glaze tests.