POTTERY (from pot. AS. putt, pot. from Ir. pots, plate, Welsh pot. Bret. pod, pot; connected with 0 Ir. 61, drink, OPruss. pout, Lat. potarc, colic Gk. VCSPEIP. pOnrin, Skt. pa. to drink). Pottery, in the common use of the term, is any kind of ceramic ware which is not especially designated by a name indicating its peculiar prop erties. ( See BRICK; FAIENCE; :%1 ()LICA ; PORCE LAIN TERRA-COTTA.) A more proper use of the term would be a general one, covering all kinds of wares which are made of clay or clay like substances and fixed by firing at a high tem perature.
OiAxeFaCTeRE. The dough-like condition into which clay can be worked with water and the hardness it may lie made to acquire by burning are qualities which have been turned to account by man from the earliest times, and it is upon these that the potter's art essentially depends. If a piece of clay be examined, it will be found that it consists of exceedingly minute particles. held together by aggregation when moist: hut if dried it can be easily reduced to an impalpable powder by mere pressure; and if, instead of dry ing, we add an excess of water, it may be so mixed and held in suspension in the water that it appears almost to be dissolved. In time, how ever, it is deposited as a sediment, and when the excess or water is removed, it is a soft tena cious paste, which is so non-elastic that it will retain the smallest impression made hi it with out change. This minute division of its particles and the absence of elasticity are its most valu able qualities. Clay also contains water in chemical combination, and this, once expelled by the process of baking, cannot be replaced. Hence it is that while sun-dried bricks, o• adobe, perish in a moist climate, burnt bricks are imperishable. Burnt clay, however finely ground and thoroughly mixed with water, never regains its plasticity. Clays are not of the same purity and quality: the commonest is that of brick fields, which is one of the most abundant substances in nature; but it is so mixed up with iron and other foreign in gredients that, except for bricks, tiles, and the coarsest kinds of pottery, it is not used by ad vanced peoples.
The purest kinds of potter's clay are called kao lin(q.v.). Pipe clay and potter's clay are more abundant than kaolin. They contain more silica and iron oxide, which gives them their yellow or brown appearance when fired. The general process
of preparing clay for the potter's use is described under CLAY. In preparing the finer materials for porcelain, many other operations are required, all having the same object—the extremely minute division of the substances used.
Pottery is grouped into three general classes, according to its color and texture, which in turn depend upon the quality of the clay from which they are made. These are earthenware, stone ware, and porcelain. Earthenware includes the coarsest kinds of porous ware, such as flower pots. It is opaque. adheres to the tongue, and can he scratched with a knife. It demands a low temperature in firing, as great heat reduces it to a shapeless mass. If glazed, an opaque or colored glaze is used, or a layer of finer clay is spread over the surface before the glaze is ap plied. When an opaque coating formed with tin is applied, the ware is called faience (q.v.) and Delf or Delft ware (q.v.), and when Italian in origin, mezza-majUlica, and in its finest pro ductions, majolica (q.v.). There are other fine forms, having the soft, porous texture of earth enware, but white and covered with a trans parent glaze of which the most conspicuous ex ample is Wedgewood's `Queen's ware,' When the ware is baked much harder and is vitrified. throughout, it is called stoneware.
For making vessels of circular form, the pot ter's wheel was used in all times until the intro duction of castings, and is still used very largely. This implement is a revolving horizontal disk on which the lump of clay is 'thrown,' and this lump is shaped by revolution. The disk is revolved by a treadle which the workman operates with his foot. and which is turned through a few degrees of the circle or more rapidly through the whole circle, as conditions require. Into the lump of clay the potter thrusts his thumbs, and by draw ing them upward and outward he rapidly reduces the whirling mass to the form of a vessel, the walls of which are drawn up between the fingers and thumbs. The inside is smoothed by pressing a wet sponge against the surface and the outside by a strip of leather, while the vessel is revolv hig. It is now released from the disk by means of a piece of wire which cuts the clay from the wood, and is then put on a board to dry; when dry, the form may be perfected by turning in a lathe, not unlike the implement used for wood turning.