A sodium-calcium-borate compound used as a low temperature flux which helps prevent crazing. Can act somewhat as an opacifier. Standard substitute for Colemanite. A complex calcium borate composed
of colemanite (a calcium borate), ulexite (a sodium calcium borate), shale (a clay/feldspar) and limestone (calcium carbonate). Gerstley is a powerful flux used as a lead replacement for temperature ranges
below 2000°F. The Gerstley Borate mine was closed in 2000 and while the mine is no longer actively producing, Laguna Clay Co. predicts that the stock pile of crude GB will last another 8 to 10 years (from 2006)
if current levels of usage stay the same.
