The rings employed in enamelling are generally made of a mixture of pipe - makers' clay and Stourbridge clay, rolled up In 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. Each ring is about 1/4 in. in thickness, and the same ill depth. The tipper side is prepared for use by rendering it slightly concave, which is done by rubbing it carefully upon a half - globe of lead, sprinkled over with fine sand. The under side is nearly fiat. Through the convexity thus given to the rings, the edge of the copper or dial - plate only is suffered to touch, by which means the enamel on the back is undisturbed, and the edges are prevented from sticking by rubbing over the surface of the rings with soft chalk or whiting.

The "first coats" having been placed carefully on, the rings 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 workman, and is commonly about 3/4 in. in depth. All the moisture is then slowly evaporated from the enamel by placing the cover upon a stove, or in some other convenient situation near a fire, where the evaporation can be conveniently regulated; for, should the water be dried off too quickly, the work will be in danger of spoiling from "blebs or blisters." These are very small air - bubbles, which, by rising to the surface of the dial - plates, destroy their smoothness and beauty. They appear to be occasioned partly by want of due care in laying on the enamel, and partly by the confinement of the air that the water contained, which, in the process of firing, becomes rarefied, throwing off by 'ts expansion a portion of the surrounding enamel, yet not entirely escaping without a vivid heat, and even then resolving into black or green specks, so coloured by the oxidation of the copper.

The firing is executed beneath a muffle placed in a small furnace ignited with coke and charcoal. The furnace being brought up to a sufficient degree of heat, the first coats are taken separately from tin covers, 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, to speak technically, it "runs," and on becoming properly consolidated! the first coat is completed. Great attention is required in this operation to prevent the enamel from being over-fired, as in that case the glass would lose some portion of its opacity, and other defects also be produced, to the detriment of the work. The planches are placed towards the further extremity of the muffle by means of a pair of spring tongs, and as soon as the fusion seems to take place, are turned carefully round, in order that every part should be equally fired. The planches are generally made circular, and slightly concave, for the convenience of moving the work without danger of shaking off the enamel before it becomes fixed by the heat.

As all solids, when reduced to a granulated state, occupy a greater space than before, it will be found that a very considerable depression takes place in the enamel of the first coat by the action of fusion. This deficiency in substance it is the office of the "second coat" to supply. When the work is cooled, therefore, the scale is wholly removed, on the projection round the edge of the copper and round the holes, by means of a smooth file or by a piece of greystone, and being then washed and dried, each plate is put upon a small round wax block of sufficient bulk to be held in the hand, and about 4 or 5 in. high. The feet of the dial are then either pressed firmly into the wax which covers the end of the block, or the plate is otherwise fixed by means of 3 small cones of wax placed triangular - wise on the block, care being taken not to spread the enamel by too hard a pressure. 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 replaced upon the rings, and, the moisture being evaporated in the tin cover, they are ready for a second fire.

It should have been mentioned that one edge of the cover, both in this and the preceding operation, should be left a little open to give issue to the steam.

The second firing requires equally cautious management. The plates must not be over - fired, nor must the heat be suffered to melt the enamel too rapidly, but a kind of rotary motion - technically 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 is complete, a proper knowledge of which can be gained only by experience. The work is now in a fit state for polishing.

Polishing in the art of enamelling has a twofold significance. It not only means to render bright - according to the common acceptance of the term - but also to make even, without any reference to glossiness. The enamel has a natural brightness of surface acquired from the fire, and when this is removed it is only necessary again to expose it to due heat to cause it to assume its former lustre. Yet as this brightness exists independently of evenness, and as evenness is essential to the perfection of enamelling, it is requisite in most cases to produce that quality by the method next to be described.

The materials used in polishing what are technically known as "glass plates," are greystones, ragstones (sometimes called burrs), bluestones, and fine silver sand and water. The plates are first taken separately, and the thin edges are ground off by one of the grey - stones till they become smooth and equal. Either the greystone or the ragstone is next employed, according to the nature of the work, to grind away all the irregularities which may be on the surface of the enamel, the ragstone being principally used for the more common kinds of dial. This is done in different ways': first, either by holding the plate upon the fore and middle finger of one hand, and giving it a sort of circular motion by means of the thumb, while with the other hand the polishing stone is rubbed with a forward and backward motion over every part of the surface; secondly, holding the polishing stone on the work - bench with one hand, and with the other rubbing upon it the face of the enamel; or, thirdly, by fixing the plate upon a cork, either by means of the feet or with a piece of wet flannel, and with the fingers giving it a kind of a rotary motion while the polisher is rubbed over it in a similar manner.