David Finkelnburg on thu 24 feb 11
Lisa,
I'm sorry you have had such serious glaze settling problems. Fritted
glazes are particularly prone to this.
Mel didn't mention, and I haven't seen it mentioned, that there is a
practical limit to the amount of bentonite one should add to any glaze.
What is that limit? Well, that depends on how much clay, if any, is alread=
y
in the dry glaze. So, testing is required. In general, you will use
somewhere between one-half and 3 percent bentonite (as a percent of the
total other dry ingredients in the glaze recipe).
What's the issue if you exceed the bentonite "limit?" The glaze will b=
e
slow to dry on the pot. By slow, I mean it can stay glossy and runny for 1=
0
minutes or longer in extreme cases and 3% can be extreme in some recipes.
Ideally the glaze (applied to porous bisque) will lose its gloss in 10
seconds or so. As you know, it can't be handled until the gloss is gone.
An easy way to test is to take water from the settled batch and use tha=
t
to mix in the blender or any other separate container. If you don't have a
blender, just let it slake, undisturbed, for a minimum of 24 hours before
mixing it. Add bentonite to water, not the other way around.
Good glazing!
Dave Finkelnburg
http://www.mattanddavesclays.com
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