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fire. The chlorides cannot be prevented, but will wash off fairly easily. Calcium sulphate, however, is difficult to remove without the use of acid. The sulphate scum can be prevented by adding a barium salt to the body mixing. The insoluble barium sulphate cannot dry out. An insoluble chloride is of course not commercially feasible. Efflorescence on a glazed surface means the decom- position of the glaze. Increase of alumina content is the probable remedy. Shelling is sometimes mistaken for peeling, but the term should be applied to the faulty adhesion of the glaze through a dirty or greasy surface of the body, or through the use of too infusible a glaze. The glaze thereby strips off in pieces. Creeping, or crawling, unless due to a greasy body, occurs most frequently in immature matt glazes, or in glazes composed almost entirely of frits. The glaze has never been sufficiently fluid to form an even surface after slight separations of the glaze powder have been caused by the expulsion of moisture from the body and glaze. The adhesion of a frit may be increased by adding 2 or 3 per 74 CERAMIC CHEMISTRY. cent, of china clay in the grinding. Matt glazes may be cured of creeping tendencies by the addition of a little gum to the slop, or by a suitable composition of the glaze. Dolomite is alleged to be useful as a raw material in this respect.