Borates are commonly used in glazes to protect ceramic tiles used for wall and floor tiles.  The main benefit of the use of borates in glazes is to lower the coefficient of thermal expansion which means the glazes are not as sensitive to exposure to high or low temperatures.  Also, borates reduce the surface tension of the glaze which enables it to flow evenly on the ceramic substrate resulting in a higher gloss surface.  Borates also act as a flux for other oxides allowing a lower melting temperature, especially the coloring oxides from the transition elements.  Borates also increase the chemical resistance of the surface and the mechanical durability of the product by increasing the scratch resistance and overall strength of the product.