ENAMELLING. The art of covering plates of metal with enamel is of great antiquity ; it was practised by the Egyptians, and by them probably transmitted to the Greeks and Romans. Several ancient specimens of curious workmanship prove its existence in Britain at a very early period. It was for merly employed chiefly for ornamental purposes, but since the invention of clocks and watches, its usefulness has been proportionably increased. For clock and watch dials there is probably no substance that could be substituted that can equal enamel in permanence and beauty. The art of dial-plate enamelling is divided into two branches, namely, hard enamelling, and soft or glass enamelling. In the first branch the Venetian enamels are chiefly em ployed; in the last the English or glass enamels. The practice of hard enamelling requires more skill, time, and labour, than the others, and is con sequently the most esteemed. The metals to be enamelled on are usually gold, silver, or copper; but the process being similar, one description will suffice. The copper, which is the metal usually employed, being evenly flatted in long slips, and to a proper thickness, pieces are cut off for use according to the size wanted ; they are then annealed in a clear fire in order to make them suffi ciently pliable to take the required forms which are given to them by means of brass dies. A complete set of dies varies in size from about three-fourths of an inch, to two inches and a half, the gradations being very small. The copper is next placed on the die best adapted for the purpose, and the eye, or centre hole, is made with a small round-headed punch, and smoothed with a grained file ; it is then again placed on the die, and pressed gradually open, till it nearly fills the hole with an oval burnisher ; it is afterwards pressed tighter into the hole with a round broach, the burr being occasionally taken off by the file, and care employed to prevent the eye from cracking. The punch, burnisher, and round pin, are all of steel ; the two latter taper in regular gradation towards the handles. When the eye is completed, the edge of the copper is cut round, so as to leave a small part projecting beyond the die, which is then turned up or burnished against the edge of the die, the copper being first laid smooth and flat by the burnisher. The copper is then gradually set up to the convexity or height required by rubbing it gently, yet firmly, with a bent or setting spatula, formed of a thin slip of steel about five inches long, properly fixed, after which the feet are soldered on. The inconveniences that attended the use of plain copper wire, soldered with spelter for the feet, are now entirely obviated by employing copper wire plated with silver. The feet must be cut by fixing an iron peg into the work-board ; to the pieces of plated wire being held against it, it will be found to form a very good resistance against the action of the file. It should be observed, that if coppers are to be made for flat plates, the feet should be filed at right angles; but if the plates are convex, they should be filed at an angle as nearly as possible corresponding with the curve formed in the hollow part of the copper, because when the foot is placed on the copper it will be found to stand perpendicular to the base line or edge of the copper. In order to make the feet remain in their places, and facilitate the soldering, the end of each foot, before putting it on the copper, which is done by means of a pair of corn tongs or tweezers, is dipped into a slight wash of borax and water, through which it adheres with sufficient force to admit of its being exposed to the power of the blow-pipe. The lamp in common use contains from a pint to a quart of oil, and has a cylindrical spout projecting l about three inches, being an inch or more in diameter. This space is filled ' with cotton, which being • hted, a strong flameis produced. The copper is care fully placed upon apiece o solid charcoal, long enough to be held in the hand ; and the flame being then propelled by the blow-pipe against the solder or silvered wire, as the case may be, the feet are firmly united to the copper. The whole is then thrown into the pickling-pan, in order to free it from the scale or oxid able acquired from the heat. The coppers being thus prepared, the
next process is that of enamelling, properly so called. The operations of hard enamelling, and glass enamelling, are, to a certain extent, the same. When they are different, we shall describe the difference as we proceed. The enamel, as it comes from the makers, is generally in small cakes from four to five or six inches in diameter. It is first broken with a hammer, and then ground in a mortar, and moistened with water; after which, the coppers having been first cleansed by the pickle, and carefully brushed out with water, are spread, face downwards, over a soft cloth, or smooth napkin, and a thin layer of hard enamel, called in its ground state the backing, is epread over the under sides with the end of a quill, properly cut, or with a small bone spoon. The coppers are then slightly pressed on by another soft cloth or napkin, which, by imbibing some portion of the water, renders the enamel sufficiently dry to be smoothly and evenly spread with the rounded side of a steel spatula. The next opera tion is to spread a layer of glass enamel over the upper aides of the coppers, called the first coats. In doing this, the surface is first brushed slightly over with a small camel-hair brush, or a hare's foot, to remove any dirt or extra neous particles of enamel, as the mixture of any hard enamel with the glass would infallibly spoil the work. The glass is then spread upon the coppers in a layer, the thickness of which is commonly the same as the height of the edge and eye. The water is afterwards slightly absorbed with a clean napkin, smoothly folded, and the enamel spread by a thin fiat spatula, till all uneven ness is removed, and the surface lies regularly from edge to centre. The next department is faring, as it is technically called, which consists in melting it till it becomes one uniform mass on the surface of the copper. In doing this, the first coats are placed uponrings, which are generally made of a mixture of pipe-maker's clay and Stourbridge clay, rolled up into the form of cylinders. and turned in a lathe by means of a cylindrical piece of wood forced through the centre of the mass when wet. They are next put into a shallow tin vessel called a tin cover, which is either made square or round, according to the fancy of the artificer, and is commonly about three quarters of an inch in depth. All the moisture is then slowly evaporated from the enamel, by placing the cover upon a German stove, or in some other convenient situation near a fire, where the evaporation can be properly regulated. The firing is executed beneath a muffle placed in a small furnace, ignited with coke and charcoal. The fur nace being drawn up to a sufficient heat by means of a register the first coats are taken separately from the tin covets and placed upon thin planches of clay, or iron chalked over, and gradually introduced beneath the muffle, where, in a very short time, the enamel melts or rum and becoming properly consoli dated, the first coat is complete. A second layer of ground enamel is then gently spread with a quill, and prepared for firing by the napkin and spatula as before; after which the second coats are placed upon the rings, and the mois ture being evaporated in the tin cover, they are ready for a second fire. This requires an equally cautious management as the former one. The plates must not be over-fired, nor must the heat be suffered to melt the enamel too rapidly, but a kind of rotatory motion, called coddling, must be given to the work, by holding the loaded planch lightly with the tongs, and gently drawing the edge of it towards the mouth of the muffle, and then returning it to its former place, till the fusion be complete. The work is now in a fit state for polishing, tech nically called using of. This is performed by rubbing the surface of the plate on a grit stone with fine sand and water, until all the glazed appearance is completely obliterated, and one uniform and equally rough surface is produced. The intention of this part of the process is to remove the mottled appearance, on the surface, and give a more equal convexity to the plate.