The only other way of producing this ware is by casting, which is simple as those already described, and regarded by some as producing vessels of greater elegance.
pulp is poured into a mould of plaster tilt the cavity is quite full, That part of the pulp to the mould, which must be of a certain degree of dryness, is absorbed, leaving the clay or sediment on the surface of the mould of considerable consistence. The liquid part of the pulp is now poured out ; that which remains bacomes rapidly stiffer, and in a few minutes, the moulds being removed, the vessel is completely formed, its exterior being the exact shape of the mould, and its thickness in proportion to the time allowed to the operation. These vessels, after being polished and receiving handles, &c. if thoug .t neces sary, are transferred to the stove ; and as, in the former in stances, are, when sufficiently dried, ready for the kiln to be converted from a soft and tender state to a hard sub stance called biscuit.
The next step of the process, therefore, is the subjecting of these vessels to heat in the kiln; a building of a cylin drical cavity, with a flattish dome, differing somewhat in its external, and a little in its internal, arrangement from the furnaces described under the article PORCELAIN, but conducted so much on the same general principles, that any minute description of it here would be unnecessary. The vessels are here, as in the porcelain manufacture, put into cases or saggars, and arranged in piles, leaving suffi cient interstices for the flame to insinuate itself equally in all directions. The fire is continued from twenty-four to about forty-eight hours ; the saggars are not removed till perfectly cool ; and the ware, when brought from the kiln, is termed biscuit ; a state in which it is unfit for use, being so permeable as to be accessible to water and other liquids. In making the commonest stoneware, however, it. may be remarked, that the vessels are placed in the kiln, exposed to the naked fire without being defended by saggars.— This property of earthenware, it may not be improper to state, has been applied to the construction of vessels for cooling wines and other liquids, it having been ascertained that the water, by passing constantly from the inner to the outer surface, is carried off by evaporation more hastily than could be done on any other principle.
Before this permeability, however, is removed, which, as shall be shown, is accomplished by glazing, the vessels are to be printed, a process that muat be performed while they are in a state of biscuit. The designs are engraven on copper-plates, and prints taken frola these, as in com mon copper-plate printing. The surface of the paper meant to receive the impression must be rubbed with soft soap. The colouring, whatever be its hue, is, when diluted with some colourless earthy matter, ground up with boiled linseed oil, until its consistence, when laid on the plate, be that of soft paste. The paper, covered, as just stated, with a thin coat of soft soap, is now laid on the plate, and passed through the rolling press. The printed parts of the paper, cut out and moistened, are applied to the biscuit, and the colouring matter is immediately absorbed by the porosity of the biscuit. The paper being washed from the biscuit, the colour will now be seen very distinct and regu lar on the surface of the pottery. The colour is generally made of oxyd of cobalt, which makes the figures of a bluish hue; a colour which causes the white of the ves sel to seem more pure and beautiful. This kind is deno minated the blue and white ware, and constitutes an im portant branch of the Staffordshire manufacture. A small mixture of the oxyds of iron and manganese imparts to the figures a dark colour; which is sometimes done, and has by no means an inelegant effect Printing, it may be ob served, was formerly performed after glazing; in which case they had again to be subjected to fire, as in the porce lain manufacture. In some potteries, pencilling, that is, laying on the colour with enamel, after the glazing, was, at one time, practised to a considerable extent; but this mode, being very expensive, is now comparatively disused.