o r sub 2 o 1 91 29 9 0 0639 0 184na sub 2 o r sub 2 o 2 62 62 0 0 0423 0 122minor impurities minor impurities trace n a n a n atio sub 2 fe sub 2 o sub 3 amp mgo tio sub 2 fe sub 2 o sub 3 amp mgo__________________________________________________________________________ in establishing the empirical formula for a glaze the formula is 34 normalized 34 so that the sum of r 2 o and ro is brought to unity in example i the sum of ro plus r 2 o equals 0 347 mole dividing each of the 34 moles 34 obtained by the total moles of ro and r 2 o establishes the empirical formula for the glaze given in the last column as 34 normalized mole fraction 34 by means of the empirical formula the calculation of batch weights or the determination of the proportions of ingredients required to produce a glaze having a given formula is simplified especially if it is desired to formulate the glaze from compounds other than oxides such as for example carbonates comparison of glaze formulations is thereby greatly simplified thus there is achieved according to the present invention a lead free ceramic glaze which can be fired at.