Dial - plate enamelling includes the manufacture of watch and fine clock dial - plates, with fluted plates for enamel painting, and is divided into 2 branches-hard enamelling, and soft or glass enamelling. In the first branch, the Venetian enamels only are used; in the last, the English or glass enamels. The practice of hard enamelling requires more skill, time, and labour than the others, and is consequently esteemed the most. In preparing the metals to be enamelled on, whether they be of gold, silver, or copper, the process is similar, and one description will suffice for the whole; and first of the making of watch - dials.

The copper plates having been prepared to the necessary shape and size, and an edge raised round the holes, and on the outside circumference, to prevent the enamel from spreading when it is m its soft state, the coppers are then thrown into a pickle - pan in order to free them from any impurities which may be on the surface. This pickle is composed of oil of vitriol, sufficiently neutralized for the purpose with water; or diluted nitric acid may be used. The coppers being thus prepared, the next step is that of enamelling. When the operations of hard enamelling and glass enamelling are dissimilar, the difference will be described; but to a certain extent they are the same. The enamel as it comes from the maker is generally in small cakes, 4 to 6 in. in diameter. In preparing it for use, a small hammer is used, having one end flat and the other of the shape commonly employed to rivet with. With this the enamel is broken into thin pieces or flakes, by striking the edge of the cake smartly as it rests upon the fore - finger of the left hand.

The pieces are then put into an agate mortar, and with a pestle of the same material are finely pulverized, the splinters being prevented from flying about by keeping the enamel covered with pure water all the time the process of grinding is going on. The point at which it should be discontinued can only be ascertained by experience, as the different kinds of enamel and the different modes of its application require the ground enamel to be either more or less fine. In general, it may be stated that the "backing" should be much finer than the first coat, the second coat of an intermediate fineness, the hard enamels considerably finer than the glass, and the flux somewhat finer than these, as the first operates with much less effect on the flux than upon either of the former substances.

When grinding, great care must be taken to keep the enamel free from dirt, and the light flue which arises must be washed away, 3 or more times as may be necessary, in the course of the operation, till the water comes off quite clear. A small teapot is commonly used to pour the water from, and when the enamel is ground sufficiently, the produce is emptied into some other small cup for use, the surface being kept just covered with water. The manner in which the grinding is performed is by pasting the mortar upon the work - bench, on a coarse piece of flannel or linen, twice or thrice doubled and wetted to prevent its slipping. The handle of the pestle is then grasped firmly about the middle with one hand, and the palm of the other being placed upon the top, the operator inclines the upper part of his body over the mortar, and crushes the enamel by pressing forcibly with his breast upon the hand which covers the pestle. The motion is repeated in quick succession, till all the larger pieces are reduced into coarse uneven grains, which grains are afterwards ground to the necessary fineness by holding the mortar firmly down with one hand, and with the other giving a circular direction to the pestle, using at the same time as much strength as can conveniently be exerted.

In enamelling watch - dials, many coppers are usually prepared to go on at once - that method possessing the threefold advantage of saving time, materia], and labour. After the enamel has been ground, and the coppers cleaned by means of the pickle, and carefully brushed out with water, they are spread face downwards over a soft half - worn cloth, or smooth napkin, and a thin layer of hard enamel -called in its ground state the "backing"- is spread over the under sides with the point of a quill, properly cut for the purpose, or with a small spoon. The coppers are then slightly pressed on by another soft cloth or napkin, which, by imbibing some portions of the water, renders the enamel sufficiently dry to be smoothly and evenly spread with the rounded side of a steel spatula. The water is then again dried out by the napkin, and a yet further evenness produced by going over the enamel as before with the spatula; and these operations are continued till the back becomes completely smooth, and the enamel is of an equal thickness all over. It must be observed that the water should not be entirely absorbed, as in that case the enamel would fall off in powder before the subsequent operations were completed.

When the enamel is properly spread, the loose particles are carefully cleaned away from the edge and hole, or holes, in the coppers; from the former by the spatula, from the latter by twisting around it the pointed end of a quill; and the process of laying the bottoms is thus finished. Some slight variations from the above method are in use among different artists, but the difference is scarcely important enough to require description. In some instances the enamel is laid on the spatula itself, and the coppers, instead of being held between the fingers, are placed on a round pin by means of the centre holes, till the backs are duly spread. In both modes due care must be taken that the coppers, are not bent out of their proper forms.

The next operation is to lay the" first coats"; that is, to spread a layer of glass enamel over the upper sides of the coppers. In doing this, the surface is first brushed slightly over with a small camels hair brush, or a hare's foot, to remove any dirt or extraneous 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 copper in a layer, the thickness of which is commonly the same as the height of the projection round the edge of the copper, and round the edge of the hole. The water is afterwards slightly absorbed with a clean napkin, smoothly folded, and the enamel spread by a thin fiat spatula, till all the unevenness is removed, and the surface lies regularly from the edges to the centre. The edge then being gently tapped 2 or 3 times at different places with the spatula, the water rises towards the top, and is again dried off with the napkin, when the enamel is once more made smooth by the spatula, and the water being wholly taken up by the napkin, or as nearly so as can be effected without disturbing the enamel, the first coats are placed upon rings for firing.