Method of grinding the Venetian Hard Enamel, for the Bottoms or under Sides of the Dials.
This enamel is to be broken with the hammer in.the same manner as the glass enamel; but, instead of break ing it clown in the agate mortar, it should be done in one made of iron, of a cylindrical form. The bottom of the mortar should be faced with steel, possessing a small olegree of that the enamel may return to the centre after each blow. The pestle should be about one inch and a fourth in diameter, and about six inches long, with the face of steel, about one inch and a half in diameter, and a little convex, to suit the mortar. The depth of the mortar should be about four inches ; and with respect to thickness, as there will be no strain upon the sides, the lighter it is made the better. It should also he observed, that the arris of the face of the pestle should be rounded, so as to leave no sharp edges near the part where it comes in contact with the ena mel, as they would be soon broken off, and spoil the other part of the face. After the enamel has been broken with the hammer, it must be put into the steel mortar in small quantities, and pounded till it is as fine as the glass enamel, (when it has been broken down in the agate mortar); it should then he put into the agate mortar, and ground till it appears to be reduced almost to an impalpable powder. It must be remembered not to wash the enamel that is to be used for bottoms, as the flour will, in this case, be more serviceable than de trimental. When this enamel is ground, put it into a clean gallipot, and always keep it covered with water ; for observe, if ever it gets dry after it is ground, it will be necessary to give it two or three turns in the agate mortar, otherwise the enamel is likely to blister in the fire.
Method of grinding and pickling the Venetian Hard mel that is to be used for the Tops of Dial Plates.
When a piece of enamel is chosen for hard plates, great attention should be paid to the colour, that which is the whitest being considered the most valuable. The piece that is to be ground must be laid upon a clean planch (or, what would be much better, a thin plate of platina,) and placed under the enameller's muffle till it is red hot ; it must then be quickly drawn from the fire, and quenched in very clean spring water. This
will cause the enamel to fly into very small pieces, which must be collected and put into the agate mortar. The intention of breaking the enaMel in this way, is to do away, as much as possible, the necessity of using the hammer and steel pestle ; because, if any small particle of the steel gets into the enamel, it will cause much trouble to get it out. The method of grinding it is just the same as that employed for the other hard ena mel, excepting that this must be rather coarser ; and great care must be taken, when the enamel is washed, not to throw away the water which contains the flour, which may be collected after it has settled, and put into the gallipot with that which is to be used for bot toms. When the enamel is ground fine enough, it must be put into a wide-mouthed glass ilbttle with a glass stopple, and covered with strong nitrous acid ; and in this state it should remain till wanted for use.
Method of enamelling with the Soft Glass Enamel.
The napkin that is to be used for laying or spread ing the bottoms, must be laid on the work-board four times doubled. The copper is to be held in the left hand, with the feet upwards, and a small quantity of the hard enamel fur bottoms is to be Liken out of the gallipot on the cnd of the bottom spatula, and spread roughly on the copper, covering it up to the feet and centre holes. It must then be laid between the folds of the cloth till a little of the water is absorbed, when it must be smoothly spread with the convex side of the spatula. If too much of tne water is not ab sorbed, it will be found that the enamel may be very easily removed from the parts where it Tics thickest to those that are too thin, tilt a general CVLIMCS:, is pro duced. It then be smoothly spi cad, by drying it more with the napkin, and spreading it aoaii with the spatula, observing always to bear proportiohp.ly lighter as the enamel gets drier. The centre h&c !Joist be cleared out by twisting the quill in it till it brings out all the enamel that is in it, and the operation of laying the bottom is complete.