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translucent, on metal ; (6) opaque glazes on pottery ; (c) clear glazes separated from a pottery body by a non- transparent undercoat or engobe. Enamelled brick dates from Babylonian times. Enamelled metal is not found before the Roman dominion of Egypt it is probably of Indian origin. The opacity in early enamels is due to an excess of the colouring agent over what the flux will dissolve. Thus the black enamel of Egypt and Greece may be reproduced by firing equal parts of natural magnetite with a flux made from 55 parts of sand to 45 of soda ash. The undissolved iron oxide here renders the enamel opaque. Artistic enamelling on metal and pottery was practised in England at Battersea in 1730, though a previous attempt to transplant it from Limoges had been made in the Middle Ages. The earliest known English patent for cast iron is that of Hickling in 1799. Chemically, an enamel does not differ from a glaze, though the suspended material may slightly alter the coefficient of expansion and fusing point of the glazes. Enamelling pottery is therefore not appreciably different from glazing pottery, and it is performed in precisely the same way. But enamelling metal is rendered more difficult through the disparity in coefficient of expansion between metal and enamel ; and also because the potter cools his ware slowly, while the enameller immediately exposes his to normal temperatures. Industrially, the