POTTERY, the manufacture of earth. en ware, or the art of making earthen vessels. The inferior kinds of porcelain, or pottery, are,prepared by the same pro cess as that which has been described under the word PORCELAIN; less pure, but more fusible materials being employ. ed, and, of course, a less degree of heat being applied.
The better kinds of English stone-ware are composed of pipe-clay and pounded flints. The yellow stone-ware is made of the same materials, in other proportions. The first is glazed by throwing sea-salt into the furnace in which it is baked, when the heat is strong; the salt is con verted into vapour, and this, being applied to the surface of the stone-ware, vitrifies it, and forms an excellent glazing. The yellow stone-ware is glazed by dipping the baked ware in water, in which is sus pended a mixture of pounded flint, glass, and oxide of lead. In the glazing of so me kinds of stone-ware, oxide of tin enters into the composition with the oxide of lead, and gives a whiter glaze. All the coarser kinds of pottery are glazed with oxide of lead ; this promoting so much the fusion and vitrification, that the low heat at which they are baked is suffici ent.
The wheel and lathe are the chief, and almost the only, instruments used in pot tery ; the first for large works, and the last for small. The potter's-wheel con sists principally in the nut, which is a beam, or axis, whose foot or pivot plays perpendicularly on a free-stone sole or bottom. From the four corners of this beam, which does not exceed two feet in height, arise four iron-bars, called the spokes of the wheel ; which, forming dia gonal lines with the beam, descend, and are fastened at bottom to the edges of a strong wooden circle, tour feet in diame ter, perfectly like the felloes of a coach wheel, except that it has neither axis nor radii, and is only joined to the beam, which serves it as an axis, by the iron bars. The top of the nut is flat, of a cir cular figure, and a foot in diameter; and on'this is laid the clay which is to be turn. ed ittid fashioned. The wheel, thus dis posed, is encompassed with four sides of tour different pieces of wood, fastened on a wooden frame ; the hind-piece, which is that on which the workman sits, is made a littleinclining towards the wheel ; on the fore piece are placed the prepared earth; on the side-pieces he rests his feet, and these are made inclining, to give him more or less room. Having prepared the earth,
the potter lays a round piece of it on the circular head of' the nut, and, sitting down, turns the wheel with his feet till it has got the proper velocity : then, wetting his hands with water, he presses his fist or his fingers-ends into the middle of the lump, and thus forms the cavity of the vessel, continuing to widen it from the middle ; and thus turning the inside into form with one hand, while he proportions the outside with the other, the wheel con stantly turning all the while, and he wet ing his hands from time to time. When the vessel is too thick, he uses a flat piece of iron, somewhat sharp on the edge, to pare off what is redundant; and when it is finished, it is taken off from the circu lar head, by a wire passed underneath the vessel.
The potter's lathe is also a kind of wheel, but more simple and slight than the former ; its three chief members are, an iron-beam or axis, three feet and a half high, and two feet and a half diameter, placed horizontally at the top of the beam, and serving to form the vessel upon; another large wooden wheel, all of a piece, three inches thick, and two or three feet broad, fastened to the same beam at the bottom, and parallel to the horizon. The beam or axis turns by a pivot at the bottom, in an iron stand. The workman gives the motion to the lathe with his feet, by pushing the great wheel alternately with each foot, still giving it a greater or lesser degree of motion, as his work re quires. They work with the lathe, with the same instruments, and after the same manner, as with the wheel. The mould ings are formed by holding a piece of wood or iron, cut in the form of the mould ing, to the vessel, while the wheel is turn ing round, but the feet and handles are made by themselves, and set on with the hand ; and if there be any sculpture in the work, it is usually done in wooden moulds, and stuck on, piece by piece, on the outside of the vessel.