Gerstley Borate is no longer being mined, Although we have a good amount remaining, this is the last of what is avaliable to us. Gillespie Borate is the substitute for this Gerstley Borate. When we run out of Gerstley we will NO LONGER HAVE ANY TO SELL. Gerstley Borate is a natural material that is used as a melter in glazes. The material begins to melt at low temperatures, becoming a clear gloss by cone 06. Along with being an excellent melter, Gerstley is very plastic and is able to suspend glazes. Because of this, it is very common to see a glaze recipe with Gerstley Borate that has no clay content. However, the material contains little to no Alumina Oxide, which is essential in a glaze. Information gathered from Digitalfire Ceramic Materials Database .
