A substitute for mined-out Gerstley borate, a naturally occurring source of boric oxide, promoting early fusion. It is a blend of the same minerals proportioned to preserve the chemistry and working properties of Gerstley Borate. Use it as a 1:1 substitute. Testing first to compare fired results is recommended; some glazes may need minor adjustments.

For more information on Gillespie Borate borate, see the Digitalfire.com Reference Library of ceramic materials.