what is anhydrous borax
A highly concentrated source of boric oxide for glazes. Anhydrous borax is made by burning or fusing hydrated borax. It thus contains little or no water of crystallization (conversation ratio of .53 compared to hydrated decahydrate borax) and does not rehydrate under normal storage conditions. Anhydrous borax is water soluble, but considerably less so than raw borax (in aqueous solution it can provide slow release of boron).