Why would a glaze turn into a jelly like this?

Wednesday 24th June 2015

This is one of the things Gerstley insight-live.com/glossary/129">Borate commonly does (when its percentage is high enough). It is also highly thixotropic - this can be stirred vigorously to thin it, yet within seconds it turns back to jelly again. This is part of the reason it is often referred to as “ghastly borate”. Side effects of this include high water content, slow drying, excessive shrinkage on drying, cracking and crawling. To attempt a fix, I deflocculated it with Darvan. It was stable enough to dip bisque ware, with difficulty (but pieces dried very slowly). But overnight it has turned back into a gel. What can be done with a mess like this? Start over, with three options:
1. Identify the mechanism to isolate the base recipe and substitute another.
2. Replace the Gerstley Borate with an equivalent that does not do this (Gillespie Borate).
3. Do a little chemistry to source the B2O3 from a frit instead (e.g. in an account at insight-live.com).

Pages that reference this post in the Digitalfire Reference Library:

Gerstley Borate, Glaze Gelling, Getting Frustrated With a 55% Gerstley Borate Glaze

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