Potterycrafts Gerstley Borate

Gerstley Borate is an ore which contains a mixture of the minerals Colemanite (Ca2B6O11.5H2O) and Ulexite (NaCaB2O9.8H2O). The calcium borate and sodium calcium borate found in this ore offer a form of borate which is very slowly soluble in water. Constituent in raw glazes and ceramic bodies.