Since porcelain is only a finer kind of pot-.
tery, the following description, in its earlier .
portion at least, will comprehend the mode of manufacturing both kinds of ware.
The materials for earthenware are reduced to the consistence of cream, in whie state they are called slip; this fluidity is necessary to insure the perfect mixture of all the ingre dients, and their mutual chemical action in the fire. The basis of the composition is a clay from the plastic clay formation in Devon. shire or Dorsetshire, to which is added ground flint, which gives whiteness and solidity to the goods. For the better kinds, a portion of China-clay, or decomposed felspar from Corn wall, is added, together with a small quantity of ground white granite. By this means the density of the ware is increased, greater purity of whiteness is obtained, and also a degree of vitrification which makes the ware sonorous when struck. The flints employed are burned in a kiln, slaked to destroy their coherence, and ground to powder in a mill. The powder is then sifted in water, until reduced to a fit state for combination with the other substances. The clays are thrown into their several vats sunk in the ground, where they are blended with water, and sifted through fine silk lawns into other receptacles, and then diluted with water. The mingled flint and clay, in the state of a creamy liquid, is then pumped into a boiler, or Blip-kiln, the bottom of which is formed of large flat fire-bricks, under which four or five parallel flues pass from the fire place to a high chimney. Tho water is eva porated, Midi the boiling mass is brought to a proper consistency for working ; but the steam having given it a cellular and porous texture, it requires to be beaten or wedged until the air is driven out, and a section of the mass, when cut, is smooth and compact.
All the of ware, such as cream ware, drab ware, drab body, brown body, Egyp tian. black, blue body, jasper body, turquoise body, &c., are formed of different kinds and proportions of flint and clay, with small addi tions of colouring materials. Round articles,
which may be turned upon a lathe, have their form given upon the thrower's wheel, which is a lathe with a vertical spindle, having a small round table on the top, at which the thrower sits. He receives the clay prepared to the proper size by a woman, and throws it upon the whirling-table between his knees, which is put in motion by the wheel-woman, whose eye watches every motion of tho thrower, and regulates the velocity of the work with perfect accuracy. The thrower first draws the clay up into a pillar, then depresses it into a flat cake, until the whole mass has been drawn into a circular arrangement of all its parts. He then opens the hollow of the ves sel with his thumbs, and continues to draw out the clay, or press it inwards, until the desired shape is given to it. It is then cut from tjie table by a brass wire, and placed on a board, which, when full, is carried into a stove-room to harden.
When a number of vessels of the same size are.to be thrown, a gauge is fixed so that its point just touches the top edge of the article when it is revolving ; this fixes both the height and diameter of all that are made in that pattern.
When the vessels are sufficiently hardened, they are turned upon a lathe similar to that used by wood-turners. The turner dexter ously shaves away the clay to the proper thickness, and works the mouldings, &c., polishing the whole with a steel burnisher. Ho frequently ornaments bowls, jugs, &c,, with a coating of various coloured clays, which arc sometimes blended with each other, so as to give a marbled surface; by these earthy pigments he produces an infinite of patterns. This kind is called .Dipped Ware, Such articles as require handles and spouts are then passed to the handler, who makes those appendages in plaster moulds, and sticks them to the vessels with liquid clay. Plain handles are pressed by a syringe through a , hole of the proper size and form, and as the clay comes through in long strings, it is cut off, and bent into the desired shape for tho handle.