The thickness of this first layer de pends entirely upon its colour : delicate colours in general require that it should have no great thickness.
The moist enamel, being thus placed, is dried, by applying a very clean half worn linen cloth to it, which must be very carefully done, to avoid removing the enamel by the action of wiping.
In this state the piece is ready for the fire. If it be enamelled on both sides, it is placed upon a tile, or Iron plate, hol lowed out in such a manner, that the un covered edges of the piece alone are in contact with the support But if it be enamelled on one side only, it is simply laid upon the plate, or upon a tile. Two things, however, require to be attended to. 1. If the work be very small, or net capable of being enamelled on the oppo • site side, the iron plate must be perfect ly flat, in order that the work may not bend when softened by heat. 2. If the work be of considerable size, it is always counter-enamelled, if possible ; that is to say, an enamel is applied on the back surface, in order to counteract the ef fect which the other coating of glass might produce on the soft metal, when it came to contract by cooling.
The enameller's furnace is square, and built of bricks, bedded in an earth pro per for the purpose. It may be consi dered as consisting of two parts, the lower part which receives a muffle rest ing on the floor of the furnace, and open on both sides.
The upper part of the furnace consists of a fire-place, rather larger and longer than the dimensions of the muffle. The fire-place contains the muffle, and must surround it on all sides, except at the bottom. The charcoal is put in at a door above the muffle, which is closed as soon as the fire is lighted. A chim ney proceeds from the summit of the furnace, with a moderate aperture, which may be closed at the pleasure of the ar tist, by applying a cast iron plate to it. This furnace differs from that of the as sayer, in the circumstance that it is sup plied with air through the muffle itself: fbr if the draught were beneath the muffle, the heat would be too strong, and could not be stopped when requisite.
As soon as the fire is lighted, and the has acquired the requisite degree of ignition, the charcoal is disposed to wards the lower part of the muffle, in such a manner as that it shall not fall upon the work, which is then conveyed into the muffle, with the greatest care, upon the plate of iron or earthen-ware, which is taken out by long spring pin cers. The work is placed as near as possible at the farther extremity of the muffle ; and as soon as the artist per ceives a commencement of fusion, he turns it round with great delicacy, in or der that the fusion may be very uniform. And as soon as he perceives that the fu sion has entirely taken place, he instant ly removes it out of the furnace : for the fusion of gold happens so very near to that of the enamel, that the neglect of a few seconds might be attended with considerable loss.
When the work is cooled, a seond coat of enamel is applied in the same manner as the first, if necessary. This, and the same cautious management of the fire, are to be repeated for every additional coat of enamel the nature of the work may demand.
As soon as the number of coatings are sufficient, it becomes necessary to give an even surface to the enamel, which, though polished by the fire, is neverthe less irregular. This is done with a fine grained Lancashire tile and water. As the file wears smooth, sand is used. Much precaution and address are requir ed in this part of the work, not only be cause it is easy to make the enamel se parate in splinters from the metal, but likewise because the colour would not be uniform, if it were to be ground thinner at one part than at another.
The deep scratches of the file are in the next place taken out by rubbing the surface with a piece of deal wood and fine sand and water. A polish is then given by a second ignition. This polish, however, is frequently insufficient, and not as perfectly uniform as the delica cy of the work may require.