ENAMELS and ENAMELLING. There exists evidence that .the Egyptians practised this beautiful 'art; but this cannot be affirmed of the Greeks. The Romans, however, have bequeathed abundant evidence that they were acquainted With the art, and practised it 'ex tensiVely, at least in the time of the Lower Empire.
Enamels are ;ritrifiable substances, and may be divided into two kinds, transparent and opaque. The basis of all enamel is a ivhite transparent glass. The addition of some of those metallic oxides which merely impart colour, as gold, silver, copper, cobalt, &c., con vert this into a transparent enamel ; while those of tin and antimony, Which render it opaque without imparting boltiur, form a White opaque enamel. There is also a material, of which the Commercial name is glass enamel, the opacity of which arises from the presence of arsenic. This substance is very glassy, brittle, easily scratched, readily fusible, and very white : it is used for making the common kinds of watch and clock dials, ornaments for the mantel shelf, the toilet, &c.
Enamel is made in some of the English glass houses, but the best is imported from Italy. ThiS is in the form of circular cakes, measuring from about three to about seven inches in diameter, and half or three quarters of an inch in thicknesa It is cream coloured, heavy, less brittle than glass, is sufficiently hard to scratch crown glass ; its fracture is conchoidal, and exhibits a resinous lustre, and it fuses at a temperature a little below that which melts gold. It is sold at from 12s. to 20s. per lb.
Enamelling divides itself into two branches --transparent and opaque. The first is em ployed for the purpose of ornamenting gold and silver snuff-boxes, watch cases, and various articles of jewellery. Previously to the appli cation of the enamel, various patterns and devices are bright-cut with the graver or the rose-engine, when the ctits reflecting the rays of light from their bright and numerous sur faces exhibit through the richly coloured enamels with which they are encrusted a beautiful play of colours. Sometimes this
enamelled bijouterie is further adorned with paintings in enamel executed on rich trans parent grounds.
Opaque enamelling is employed in the manufacture of watch and clock dials and of plates for pictures. For this purpose the enamel is first broken with a hammer into small pieces, and then ground with a pestle and mortar formed of agate. It is then spread evenly on a plate of copper, which has been prepared for its reception, and, being passed through the furnace; the enamel is melted, and adhering firmly to the metal, thus forms an enamel plate. For the best kind of dials, a second coat of enamel is laid over the first, and for pictures a third is added. The figures are painted on the dials in a vitrifiable colour, when they are again subjected to the heat of the furnace, which melting the colour and softening the enamel at the same time, incor porates the two into one body, and thus per manently fixes the painting. Gold is fre quently used instead of copper for small enamel pictures. When the enamel plate is prepared, the artist proceeds to paint his picture in a 'similar manner to that which is pursued by the painter in oil or water colours ; a princi pal difference being, that instead of waiting for the colours to dry before proceeding to lay on another coat of colour, he has his work passed through the fire, by which process the colours are imperishably and immoveably fixed. Paintings in enamel are usually subjected to the furnace ten or twelve times, and in some cases oftener. The colours are composed of a colourless glass as a base, the colouring matters being metallic oxides. Thus silica, borax, and the red oxide of lead, form a base or flux for some colours. The habitudes of the various oxides, however, require that each should be treated with reference to its pecu liar properties : for instance, the flux which, employed with gold, is best adapted for the production of a useful and beautiful colour, is wholly inefficient if used with cobalt.