ENAMELLING. Neri on 'lass, with the notes of Merret and Kunckel, afford a variety of good receipts for making enamels, though much still remains to be done in this art. The art is indeed retarded by the considerable advantages the enameller derives from the discovery of any colour uncommonly brilliant, clear, or hard. On this account the artist na turally endeavours to keep his process a secret, as the source of private gain. The principal ingredients of enamel co lours are, however, wed known.
There are two kinds of enamel ; the opaque and the transparent. Transparent enamels are usually rendered opaque by adding putty, or the white oxide of tin, to them. The basis of all enamels is therefore a perfectly transparent and fusible glass. The oxide of tin renders this a beautiful white, the perfection of which is greater when a small quantity of manganese is likewise added. If the oxide of tin be not sufficient to destroy the transparency of the mixture, it pro duces a semi-opaque glass, resembling the opal.
Yellow enamel is formed by the addi tion of oxide of lead or antimony. Kunc kel likewise affirms that a beautiful yel low may be obtained from silver.
Red enamel is formed by the oxide of gold, and also by that of iron. The for mer is the most beautiful, and stands the fire, which the tatter does not.
Oxide of copper affords a green, man ganese a violet, cobalt a blue, and iron a very fine black. A mixture of these ena mels produces a great variety of inter mediate colours, according to their na ture and proportion. In this branch of the art the coloured enamels are some times mixed with each other, and some times the oxides are mixed before they are added to the vitreous bases.
The enameller who is provided with a set of good colours is very far from being in a situation to practise the art, unless he be skilled in the methods of applying them, and the nature of the grounds up on which they are to be laid. Many of the metals are too fusible to be enamel led, and most of them are corroded by the action of the fused glass. For this reason none of the metals are used but gold, silver, and copper. Platina has in deed been used ; but of its effects and habitudes with enamel very little can be said, for want of a sufficient number of experiments.
The purest gold, of 24 carats, is calcu lated to produce the best effect with ena mel. 1. Because it entirely preserves the metallic brilliancy, without undergo ing any oxidation in the fire. 2. Being less fusible, it will admit of a more re fractory, and consequently a harder and more beautiful enamel. It is not usual; however, to enamel on finer gold than 22 carats; and the operation would be very defective, if a coarser kind than that of its carats were used. For in this case more alkali must be added to the enamel, to refuter it more fusible, and this addi tion would, at the same time, render it softer and less brilliant.
Rejecting all these exceptions, the fol lowing description may be taken, by way of example, of fixing a transparent blue enamel upon gold of 22 carats.
The artist begins his operation by breaking his enamel into small .pieces in a steel mortar, and afterwards pulverizing it in a mortar of agate. He is careful to add water in this part of the process, which prevents the splinters of glass from flying about. There are no means of ex plaining the point at which the tritura tion ought to be given up, as this can be learned only by experience. Some ena mels require to be very finely triturated ; but others may be used in the form of a coarse powder: As soon as he ap prehends that his enamel is sufficiently pounded, he washesit by agitation in very clear water, and pouring off the fluid as it becomes turbid. This process, which is made for carrying off dust and every other impurity from the enamel, is con tinued until the water comes off as clear as it was poured on.
The workman puts his enamel thus prepared into a white earthern or china saucer, with water poured on it to the depth of about one tenth of an inch. Ile afterwards takes up the enamel with an iron spatula as equally as posible. As the enamel here spoken of is trans parent, it is usual to ornament the gold with rose work, or other kinds of work, calculated to produce a good effect through the enamel.