The clay undergoes such a preparation at the place where it is procured as to free it from stones, and the grosser impurities. When brought to the manufactory, it must be rendered still more pure ; an object which is accomplished by means of machinery. The clay having by machinery been reduced to small pieces, approaching to a coarse powder, is transferred to a vat, for the purpose of being mixed with water. By constant and continued agitation in this vat, the finer parts of the clay amal gamate completely with the water, and form a fine pulp ; while the gross and strong particles, from their gravity, remain at the bottom as refuse. The pulp is now convey ed from this vat through a series of sieves of different de grees of fineness, and moved backward and forward by machinery, till the grosser parts are entirely separated from those of which the Stoneware is to be composed.
Flint, as already men,tioned, is an indispensable ingre dient in the composition of stoneware. In preparing it, it is first placed in a kiln and raised to a red heat, when it is thrown in this state into cold water. This process is to diminish its cohesiveness, that it may be the more easily reduced to powder. The flint is now, by a process exactly similar to that described in regard to clay, reduced to a pulp, and the gross parts separated from the fine, which latter is that used in the formation of the ware. This pulp, as well as that of the clay, must always be made into a certain consistence, with a view to ascertain exactly what quantity of each is contained in a given measure. The two pulps are now mixed together in such proportions that the flint is as one o five or one to six of clay ; and they are caused to amalgamate by an operation similar to that em ployed for mixing clay and v ater, as recently described.
Flint and clay being thus mixed, the next step is to separate the water from them, which is effected by eva poration. When the operation has been continued till the substance is sufficiently dense and stiff, it is cut out in cubical figures, and subjected to a process, the object of which is to render the mass of uniform consistence, and fit for working. This result may be attained either by the hand, or more easily and efficiently by a machine formed for the purpose. The nature of this operation is simple. A mass of the consistence is taken between the two hands, and being separated is reunited with great violence, but at different parts from those at which it was disjoined. It is again separated and again united, and, as before, the points of contact must be different. This process being repeated twenty or thirty times, the mass has assumed such a uniformity in its different parts, that though it ori ginally consisted of two pieces, one black and the other brown, the colour of both at the end of the operation will be exactly and entirely the same. The masses thus mixed
and prepared, are allowed to remain some time cre they are converted into vessels, it having been ascertained that they work the more easily from continuing a while un touched while in this state.
These substances it is now the duty of the potter to form into articles of various shapes. This may be effected in one of three ways, either by throwing, pressing, or casting. The first of these, or throwing, is performed on a machine, denominated the potter's lathe, of which there are two kinds, in both of which many important improvements were made by Mr. Wedgewood. The ware to be made in this way are first roughly formed on one of these lathes, and after this operation, are allowed to dry to a certain ex tent; but when they come to what is called the green state, or to a given degree of tenacity and stiffness, they are ap plied to the other lathe, called a turning lathe. The vessels are on this lathe turned to their proper shape, and obtain a considerable degree of smoothness, and when re moved from it, are burnished with a smooth steel surface. The same degree of dryness at which the vase requires to be applied to the turning lathe, is also the proper state for fixing on the handles and other appendages. These parts, previously made and reduced to a proper degree of dry ness, are attached to the vase by means of a pulpy mass of clay mixed with water, termed slip. All kinds of mount ings, however, are formed on the wheel or lathe by apply ing to the vessel when the wheel is turning round, a piece of wood or iron of the form meant to be communicated. The juncture is sm000thed with a wet sponge. The vessels are now removed to a stove, varying from 80 to 90 degrees of temperature. Articles of a superior quality, when fully dried in this stove, are rubbed over with a small bundle of hemp, in order to smooth them thoroughly, and to remove those inequalities by which the surface may be marked.
Vessels of a circular form are the only kind made by throwing or by the lathe. Those that have flat sides, or are of an oval shape, are the result of the second method, or of pressing, which is done with moulds. The moulds, which are made of plaster, consist of two separate halves, one half of the figure being respectively on the two sides of the mould. The clay is formed into two flat pieces, of the thickness of the vessels meant to be made ; these pieces are now pressed severally into the two sides of the tnoulds ; the halves of the moulds being now brought together, the clay is also united: and after a complete juncture has been effected, the mould is removed, and the vessel has attain ed its proper shape and figure. The vessels are now polished, are, if thought proper, adorned with I onales, spouts, &c. and are removed to the stove, as in the former operation.