Chic Lotz on fri 23 sep 11
I have a ^6 Speckled Blue glaze that also turns to pudding if I
haven't used it in a long time. It too has an overload of gerstley
borate which seems to be the culprit as Bill Shran suggested. When a
glaze with a small amount of soluble alkalis becomes like pudding
after being left undisturbed, it can become too viscous. This process
is called "thixotropy." Our natural inclination is to add water to
thin the glaze, but don't do that. Instead, just stir it rapidly, with
vigor, and that should thin it for the current use without adding any
water.
In The Potter's Dictionary by Frank and Janet Hamer you will find a
complete explanation of thixotropy. They list magnesium oxide and
carbonate, alkaline frits and most wood ashes as the likely cause, but
my experience includes an overload of gerstley borate. I found that if
you keep adding water to thin it, eventually the glaze will crack all
over and fall off the pot as soon as it dries after
application........ which is difficult to remedy. They suggest a tiny
amount of sodium silicate as a remedy instead. Vigorous stirring seems
to work for me!
Chic Lotz
www.GlazeBasics.com
Chic@PotteryPoet.com
www.PotteryPoet.com
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