Page:The New International Encyclopædia 1st ed. v. 16.djvu/380

* POTTER-WASP. 322 POTTERY. baskets. These cells are filled with caterpillars, sawfly lai-va-, and the larvif of beetles, by the mother wasp, an egg being laid in each cell and the resulting grub feeding upon the stored insects. POTTERY (from pot. AS. potf, pot, from Ir. pota, piiitr. Welsh pot, Bret. pod. pot; connected with Olr. 61, drink, OPruss. pout, Lat. potare, yEolic Gk. ■n-iixeii', pOiiein, Skt. pa, to drink). Pottery, in the common use of the term, is any kind of ceramic ware which is not especially designated bv a name indicating its peculiar prop- erties. (See'BKicK: Faiexce: iI..70LiCA:. Porce- lain; Tebra-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. Manufacture. The dough-like condition into which clav can be worked with water and the hardness it may be 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 tosether by aggregation when moist; but 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 mi.xed 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 in 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 repLTced. Hence it is that while sun-dried bricks, or 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 cornmonest is that of brick fields, which is one of the most abimdant 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 peo|des. The purest kinds of potter's clay are called kao- lin (q.v.). Pipe clay and potter's clay are more abtindant 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 w-hich they are made. These are earthenware, stone- ware, and porcelain. EnrlheiiM-are includes the coarsest kinds of porous ware, such as flower pots. It is opaque, adheres to the tongue, and can be 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-majolica, and in its finest pro- duc^tions, 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 dra i 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- ing. 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. The use of 'jiggers' and 'jollies' has greatly increased the rapidity and regularity with which vessels may be shaped. A jigger is a machine carring a revolving mold in which the clay is shaped liv a former which is brought down and held firmly within the mold, the clay having been carefiillv spread by hand upon the inside surface of the mold. The jigger is used for deep dishes, vases, and the like. The jolly is a similar contrivance used in forming plates and other flat pieces. Jugs and bottles are com- monly made in two parts and cemented together before the clay is dry. The clay is usually allowed to dry in the mold, and as the water is drawn off the clay shrinks so that it does not cling to the mold. Such additions as spouts and handles are molded separately and cemented with moist clay before the pieces dry. Casting is employed in making very fine ware. The plaster-of-Paris mold is filled with liquid clay which is allowed to stand until a thin film is formed around the surface of the mold, after which the rest of the clay is poured out: this process is used for 'egg-shell' porcelain, but also, in rare cases, for fine, hard pottery. The making of these plaster-of-Paris molds is a matter of great delicacy. The model having been designed, a mold is made from it which is divided so that it mav be easily removed from the clay. This is called "the block mold. From this there is made a cast which is. of course, a rep- lica in plaster of the original model, and from this the working molds are made. After the pieces of pottery have been formed, they are taken 'to the drving-stove. where they are ex- posed to a heat of about 85° Fahr. When con- sidered drv. they are placed in great earthen-