Glaze compositions

This invention relates to boron-containing compositions for use in glaze compositions. There is provided a boron-containing composition for use in glaze production, which composition is obtainable by a process which comprises heating to a temperature sufficiently high that calcination occurs but insufficient for the formation of a homogeneous melt a mixture comprising components capable, under the conditions of heating, of forming the oxides B2O3, SiO2, Al2O3, Na2O and optionally CaO in proportions such that the relative percentages by weight of the said oxides, based on the total weight of the said oxides, are as follows: 10 to 18 % B2O3, 40 to 65 % SiO2, 17 to 32% Al2O3, 4 to 9 % Na2O, and O to 10 % CaO. The boron-containing compositions according to the present invention may be used in glaze compositions, suitably frit-free or boron-free frit-containing glaze compositions.