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Desktop INSIGHT software has been around since 1980 solving material substitution issues like this one.

But there is now a better way: An account at

Digitalfire Corporation makes no guarantees about the information contained herein. It is given as a guide along with support information to help visitors work out the problem themselves.


What is it? Why replace it?

Gerstley Borate is a ceramic glaze flux. It sources boron, and melts far better than any other common raw material. It has been a foundation material in low and middle temperature pottery glaze recipes for many years. Potters have a love/hate relationship with this material: they use it for its tremendously low melting point; they endure the problems it presents (inconsistency, gelling of the glaze slurry, crawling, micro-bubbles, boron-blue discoloration). Gerstley Borate is not used in industry because of its issues. Strangely most people have used it without knowing what it really was. And few people realize how easy it is to replace it to create much easier-to-use and less problematic glazes.

The Best Substitution Approach

Years of using substitutes have demonstrated that it is unrealistic to expect an exact duplicate (even a good one). It is better to source boron (the active ingredient in GB) from a frit (if you cannot substitute GB in a functional glaze and maintain its chemistry, it is likely unbalanced anyway). Calculating a new recipe having the same chemistry from a different mix of materials is easy (with the right software and technique). Use Digitalfire desktop INSIGHT or your account at

Here are two videos on how to substitute Gerstley Borate in glaze recipes:
One and two (from my youtube channel).

Nirvana 1 : With Ceramic Calculations You Don't Need a Substitute!
Nirvana 2 : Improve the glaze while you are at it

Learning From Some Examples

was a substitute formulated at Plainsman Clays. Although no longer actively sold, we believe it was the best available because it considered the chemistry, mineralogy and physical properties of Gerstley Borate. Its development and recipe were openly documented online and still available. Learn about specific middle temperature glazes (like floating blue, iron reds), what to do if you have problems.

Other Approaches

Substitutes have come and gone over the years. Here are a list of some. Laguna Borate, Boraq, Murray's Borate, Cadycal, Ferro Frit CC298-C, Other Frits, Gillespie Borate, Ulex Empresa Minera, Dal-Tile 439, IMCO, Ulexite, Colemanite

A Learning and Teaching Opportunity

Have we understood our materials? Have we been 'recipe junkies' for too long. There is a great educational opportunity here, why not teach your students about it?

Copyright 2000 Digitalfire Corporation