Gerstley Borate

Priced per pound. Quantity discounts are available.

Gerstley Borate is a sodium-calcium-borate compound used in ceramics as a low and mid-range temperature flux. It is essentially a source of boron in glazes, and acts as a melting agent. It also can act somewhat as an opacifier and prevent crazing. It is a conglomerate mineral made up mainly of Colemanite, Ulexite and Hectorite.

It is a standard substitute for Colemanite.

We get a lot of inquiries regarding the source of Gerstley Borate here at The Ceramic Shop. As many potters know, the source mine of this material -- located in Southern California -- became depleted in 2000, and supplies petered out over the next few years. As such, about a decade ago, Gerstley Borate became a hot and rare material. Synthetic blends such as Laguna Borate or Gillespie Borate were put on the market in an attempt to replace this lost material; these substitute materials were perfectly fine for certain things, but depending on the recipe, didn't always accurately emulate the dear departed Gerstley Borate. This is precisely why we get so many questions regarding this material; customers want our assurance that we aren't just packaging up Laguna or Gillespie Borate.

We can assure you that this is not the case -- just two short years ago, the main supplier of Gertsley Borate announced that there is still a large stock available. So, if you are looking for Gerstley Borate, and want assurance thaty oua re ordering 'the real deal', look no further than The Ceramic Shop!

The chemical composition of Gerstley Borate is:

SiO2 (14.8%)
Al2O3(0.98%)
Fe2O3-T(0.425%)
MnO(0.024%)
MgO(3.54%)
CaO(19.4%)
Na2O(3.95%)
K2O(0.399%)
TiO2(0.050%)
P2O5(0.053%)
B2O3(26.8%)
LOI(29.5%)
Trace minerals (0.079)