A cure for long-time Gerstley Borate sufferers

Wednesday 24th June 2015

These are various different insight-live.com/glossary/88">terra cotta clays fired to cone 04 with a recipe I developed that sources the same chemistry as the popular G2931 Worthington clear (50:30:20 GB:Kaolin:Silica) but from a different set of materials. The key change was that instead of getting the B2O3 from Gerstley Borate I sourced it first from Ulexite (G2931B) and then from a mix of frits (G2931K). All pieces were fired with a drop-and-hold firing schedule C03DRH. Fit was good on many terra cottas I tried (pieces even surviving boiling:icewater stressing). Where it did not fit I had thermal expansion adjustability because more than one frit was sourcing the boron. Frits are so much better for sourcing B2O3 than Gerstley Borate (the latter is notorious for turning glaze slurries into jelly!). Of course, a little glaze chemistry is needed to figure out how to convert a recipe from Gerstley Borate bondage to frit freedom, but there is lots of information here on how to do that.

Pages that reference this post in the Digitalfire Reference Library:

Ulexite, Gerstley Borate, Tried and True recipes. Really?, Gerstley Borate 50:30:20 glaze. How could this have worked?, Lead bisilicate with his ugly borosilicate cousins at a cone 05 party, Gerstley Borate 50:30:20 glaze using Gillespie Borate instead, This is how bad Gerstley Borate glazes can blister, Getting Frustrated With a 55% Gerstley Borate Glaze

This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.