A clean napkin is then to be folded in the same man ner as for laying the bottoms; but it must be laid on the board so as to hang over the edge about three or four inches ; and, to prevent its falling, it is best to put some kind of weight upon it. When the wax upon the laying block has been softened, and made of a shape fit to receive the copper, it must be placed evenly on,. and the feet pressed into the wax, till the under edge of the copper nearly touch. This will be best done by pla cing the setting die on the copper, and pressing it down, as, by this method, the shape of the copper will be preserved, and the upper side secured from the per spiration of the hands, which might prove injurious to the work, as any thing of a greasy nature is very apt to make the enamel blister. The copper must now be brushed quite clean with a soft hair brush, or hare's foot, taking great care not to leave any of the hard enamel on the surface, or about the edge. The block with the copper on it is now to be held in the left hand, and a small quantity of the glass enamel is to be taken upon the end of the flat spatula, and laid upon the cop per, near the centre hole, taking very great care not to let the water through the centre hole, as that would take the enamel from the bottom, which could not be repla ced without taking the glass from the top ; an operation that would be exceedingly dangerous, as the two kinds of enamel would get mixed together, which would in evitably spoil them both. If a careful attention is paid to what we have said, an evil of this kind need not be feared, as the enamel need not be taken out of the ba sin with so much water as to render it at all hazard ous, if it is lifted slowly, and by that means suffered to drain a little. When a sufficient quantity of the glass enamel has been put upon the copper, it must be rough ly spread, by repeatedly indenting the edge of the flat spatula into the enamel, crossing it in all directions till it lies of an uniform thickness all over the copper. The surface, in this state, will have various little inequali ties and indentations, which may be reduced by just tapping the side of the block two or three times with the edge of the slmtula. The water which this opera tion will cause to flow on the surface of the enamel, must be dried a little with the corner of the cloth, but not so much as to render the enamel difficult to be mo ved ; for the intention of drying it in this state is to take away the superfluous water that floats on the sur face. If, however, the napkin should at any time ab sorb so much of the water that the enamel could not be moved without such a degree of pressure as would loosen the feet of the copper from the wax, or risk bend ing the copper, a drop or two of water may be taken upon the end of the spatula, and applied to different parts of the enamel, till the desired effect is obtained. It rarely happens that the enamel, in this state, is so evenly laid as to want no adjusting; it must therefore be carefully observed, that the side or part which is too thick, must be reduced by removing a part to places that appear deficient. This may be done by spreading the spatula over the enamel, turning the block round with the fingers and thumb of the left hand, till it lies generally even. It must then be dried again with the napkin, and the surface made smoother, by passing the spatula over it in all directions, bearing a little harder on the enamel as it gets drier. As the rubbing and spreading the enamel in this manner will attract the moisture to the surface, and hinder the ena mel from lying so smooth as is necessary, it must there fore de dried again, and the laying finished by gently passing the spatula lightly over the surface till the ena mel lie very smooth and even.
In determining the thickness of the enamel, an al lowance must be made for its granulated state previous to melting, when it occupies a larger space than it does subsequently. The enamel should therefore be spread a little thicker than the depth of the edge and centre would seem to require. In all cases, however, it will be bet ter to have the enamel a little below the edge and cen tre when it is melted in its first fire, for reasons which we shall afterwards explain. One thing is to be parti cularly observed in enamelling the tops of convex plates, that the shoulder, which is about +th of the dis tance from the edge to the centre, should be laid some what thicker than towards the edge, because the edge being lower than the centre, the enamel when in a fluid state in the fire, will flow down to it, and will thus pro duce an equality of thickness on all parts of the cop per.
When the copper is covered, it must be carefully ta ken from the block, by gently raising it with the back of the thumb-nail, under the edge, and as near each of the feet as possible. After it is free from the wax, it may be
lifted with the finger and thumb from the block, and placed under the lid of the box, to keep it from the dust till it is wanted to be fired.
Description of the Method of Hard Enamelling.
When the copper is nicely pickled, fix it on the lay ing block, in the same manner as was directed for the glass enamelling, and lay a coat of glass enamel about two-thirds of the thickness that was directed for ma king glass plates. This must be fired till the enamel is melted down to a tolerably smooth surface ; and when cold, should any specks of dirt appear on the surface, they must be cut out with the point of a square graver whetted to a very obtuse angle. After this, the plate must be put into a solution of nitrous acid and water, just strong enough to cleanse the scale from the edge of the copper, being careful not to leave the plate longer in the solution than is sufficient to clean the edge, and washing it immediately in clean water.
Let the plate now be fixed on the laying block, in the same manner as if it were a copper, keeping the wax soft enough to admit the feet to pass into it with out any great pressure, as that might strain the ena mel, and cause it to crack in the fire. Take a small quantity of the hard enamel, thoroughly purified of the acid by several waters, and, with the rounded part of the round-sided spatula, spread it as equally as possible over the whole surface of the plate. When this is done, the enamel must be dried by laying the corner of a clean napkin upon it till it has absorbed a part of the water. It will then be in a fit state to be spread more equally over the surface of the plate; and, when it is spread nearly smooth, and of equal thickness, it must be dried again with the napkin, and the spreading con tinued for full ten minutes, or longer, pressing harder upon the enamel as it gets drier, and rubbing it in eve ry direction till it is compressed as closely as possible.
The next department of the business is firing the enamel, as it is technically called, which consists in melting it till it becomes one uniform mass on the sur face of the copper. But before we proceed to the de scription of firing, the apparatus for performing it re mains to be described.
The first is a ring used to support the edge of the dial while in the fire, so that the feet may not come. in con tact with any substance, as the motion necessary to be given to the dial would certainly disturb or loosen them. These rings are made, at present, of one part pipe maker's clay, and two parts of the real Dutch black lead melting pot, ground to a very fine pow der, and well tempered with water to a consistence si milar to potter's clay. A large lump of this mixture is placed upon a square spindle, and set by to dry a lit tle, when it is placed in a lathe or turn bench, and the rings turned out of the solid mass. The quantity placed upon the spindle may be sufficient to get two sized rings from the same mass by turning the largest size first. To prevent the adhesion of the enamel to the ring, (we mean that which is laid on the under side of the dial), one part of the ring is made like the frus trum of a very obtuse angled hollow cone, while the other side forms a plane perpendicular to the sides of the cylindrical parts. The dial being laid in the hol low side, will just touch it at the part where the cop per is bare, and thereby prevent the adhesion of the enamel. This part of the ring being well rubbed with fine whitening, will still further prevent such an evil. When the dial is placed on the ring, both are to be set on a planch, which is a fiat circular piece of fine stone, about 4.th of an inch thick, or, in default of this, it may be made of Sturbridge clay ; and, as it is necessary to turn the dial in the fire during the whole time it is melting, that it may be equally heated, the planch with the ring and dial upon it are set upon a small piece of clay, which should be moulded so as to form a segment of a sphere whose diameter may be about five inches. This being laid on the coals, under the muffle, it will be found, with a little practice, that the planch may be very conveniently turned-round on the spherical surface without slipping off, while the whole of the plate, by the change of position, will he equally heated. This last mentioned object is by enamellers called a turner. or a representation of this, and the manner of placing the other articles upon it, see Plate CCLII. Fig. 12, where all of them are shown in section, the dial in this Figure being a curved one, for a watch without a brass edge. A, is the dial ; BB the ring ; C the planch; and D the turner.