WHAT THE FLUX!
WHAT DO YOU MEAN THERE IS NO MORE GERSTLEY BORATE?
(WTF! November 2023 Edition)
Gerstley Borate is a flux and one of the main ingredients in eight (8) of The Potters’ Studio’s glazes. Gerstley Borate was formed in marshes and drying lake basins during the Miocene period 10 million years ago. Gerstley Borate is named after James Gerstley, former managing director of Borax Consolidated Ltd. It is manufactured by U.S. Borax and Chemical Corp.; the mine is located near Barstow and Death Valley, California, just east of Bakersfield. Fifteen years ago six (6) million (yes I said MILLION) pounds were discovered at the Death Valley mine and the well-known clay company Laguna took advantage of everyone else being asleep at the wheel and commandeered all six million pounds; but failed to tell others that this was all that was left in the mine.
Gerstley Borate has been a popular flux for many years, but its use has declined due to its scarcity and high cost and the fact that it contains impurities that can cause problems with glaze consistency and color. Of course, when a resource is limited it might be a good idea to let others know that one day there would be no more Gerstley and prepare them for necessary changes in glaze recipes. For whatever reason, Laguna did not sound the alarm or give sufficient warning to the ceramic community that soon Gerstley Borate would be no more.
So what happens when you discover that a critical and essential ingredient necessary to create favorite Studio glazes like Waxy White, Rusty Blue, Lipstick Purple, Red and Sea Green will soon be obsolete and no longer available? Well, you try to find a substitute or a replacement as soon as possible. That is exactly what the Glaze Guy, aka Bill, has done. He identified Gillespie Borate as the substitute or replacement ingredient.
Gerstley Borate and Gillespie Borate are both boron-containing minerals that are used as fluxes in ceramic glazes. Gerstley Borate is a naturally occurring mineral, while Gillespie Borate is a blended borate mineral that is produced by U.S. Borax. Gillespie Borate is often used as a substitute for Gerstley Borate because it has similar melting and flowing properties, but with fewer impurities. In general, Gillespie Borate is considered to be a good substitute for Gerstley Borate, but it is important to determine the proper portion because any change in the material makeup of a glaze can have an impact on its melt, fit, and durability. In other words, Gillespie Borate is not a direct substitute for Gerstley Borate.
With assistance from member DeAnna Dalton, the Glaze Guy has relied on the 9 dot test to figure out how much Gillespie Borate is needed for new recipes for Rusty Blue, Lipstick Purple, Red, and Sea Green. The two have painstakingly researched and analyzed the appropriate chemical combination substituting Gillespie Borate to achieve the right balance and crystallization to match the existing recipes. Using the Katz UMF calculator, DeAnna and the Glaze Guy have made more than 400 test tiles to recreate the recipes for the 5 Studio glazes. They have tested and tested and tested some more and have finally developed recipes exceptionally close to the originals. Their persistence and attention to detail have yielded new recipes that create glazes that are close “siblings” to the original recipes. We now have an alternative to the dwindling Gertsley Borate supply and thanks to DeAnna and the Glaze Guy, have added to our knowledge of substitution and replacement so that we can maintain the glazes we all know and love. Thanks, DeAnna and Bill, for your amazing time commitment so that we can all continue to enjoy Rusty Blue, Lipstick Purple, Red and Sea Green.