oG OX CKRTAIX ANCIENT KNAMEL^^.

upon a smooth leaJen tablet till the colours become trans- lucid and clear, and you again rub the piece of pottery upon the hone with saliva, and spread it upon a goat's skin smoothly fixed upon a wooden table ; upon this you polish the electrum until it shine perfectly, so that if one-half be made wet, and the other remain dry, no one should be able to distinguish which is the wet ])art and which the chry." Such is the mode of making these enamels, as described by Theophilus. With regard to the coloured glasses employed, we learn from the Twelfth chapter of the Second book, " De dii'ersis coloribus vitri, non translucidis — " Different kinds of glass found in Mosaic work, in the ancient edifices of the Pagans, namely, white, black, green, yellow {croceum), sapphire, red, and purple, and they are not clear but opaque hke marble, and they resemble square stones, of which are made electra in gold, silver, and copper, of which we will speak fully in their place. Divers small vessels are also found of the same colours, which the French, very skillful in this work, collect, and the blue they melt in their furnaces, adding a little clear white glass, and they make plates of sapphire of great value, and very usefiil in windows. They make the like also of the purple and green.'"' It appears then that it is to the ancient mosaics that the enameller of this period went for his store of coloured o;lass. Almost the onlv trans- parent colours to be found in remaining specimens are the blue, purple, and green, which supports the statement of Theophilus. The perfect preservation of the gold fillets, and the crystalline ai^pearance of some of the transparent enamels, would lead one to suppose that the glasses were easily fusible, and that the objects were not exposed to a very high tem- perature ; this is borne out by the presence of an opaque red enamel, in a specimen in the Museum of Practical Geology, which owes its colours to an oxide of iron, and at a high temperature would turn black."^ The metals which were used for the groundwork of these enamels appear, from the passage of Theophilus quoted above, to liave been, gold, silver, and copper, — the only pure metals which were ever enamelled. Of these, gold, from its superior ductility and beauty, was doubtless most commonly ^ I am iiwlebteil for this information to which he has allowed me free access to Sir Hfni-y De la Beclie, and take this op- tlie interestiii;; series of enamels in the portuiiity of recording the kindness with Museum of Pi-actical Geology.