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CaO 0.6 A1 2 O 3 0.4, SiO 2 3.8 ZnO 0.1 J The engobe remains as an only partially fused material separating glaze from body and hiding the latter by reason of its immaturity. In composition it is very like the earthenware bodies of North Staffordshire. It is applied to the body by dipping in a similar manner to the glaze. Let us suppose, now, that we are required to reproduce the glaze or enamel of the general molecular formula : a PbO b Na,O c K 2 d CaO e ZnO f BaO g MgO although so many bases in one glaze would be unlikely. The first step would be to multiply each quantity by the molecular weight of the oxide in order to obtain the parts by weight, thus 223a of PbO, etc. If the raw materials were theoretically pure, this would be unnecessary, as the calculations could be made molecularly. Lead oxide would then be calculated into the bisilicate frit favoured by the Home Office, and the corresponding amount of silica would be accounted for. Then the potash would be calculated into felspar, and allowance made for the alumina and silica thereby introduced. Excess of potash over