THE EFFECT OF BORIC ACID IN RAW MILLED GLAZES*

A study of the reactions between boric acid and typical ceramic raw materials in slips was made to determine the cause of raw glazes thickening upon standing. Raw zinc oxide, precipitated barium carhonate, and light magnesium carbonate were found to react deleteriously with boric acid in milled slips with thickening or “setting” occurring. This thickening does not occur in many instances when large amounts of white lead are present in the mill batch. Remedies are given which were used to overcome this increase in viscosity in commercial raw glazes by using calcined mixtures and insoluble frits.