PROCESSES or MANIPULATION.—Throwirig.—The process of " throwiag" is the application of the principle of " turning " to a plastic material, the turner's tools being replaced by the more delicate fingers of the " thrower." The main apparatus, or " wheel," consists of a horizontal disc, rigidly fixed on the top of a vertical spindle, to which, rotatory motion can be communicated, In addition to the wheel, the thrower has a balance, in which the pattern to be reproduced is counterpoised by the lump of clay from which the reproduction is to be made. The pattern generally only bears a very slight resemblance to tbe finished article, as ware is now seldom finished on the wheel, but subsequently passes through the turner's hands, by whom it is sometimes reduced to one-half its original substance. As a rule, except in the case of fine stone-ware, the " thrower " gives the inside form only, and leaves the outside to be fashioned by the " turner." A box to sit upon, a basin full of water, a movable gauge, with a borizontally-revolving needle or pointer conveniently placed for comparison with ware during manipulation, together with a few pieces of thin horn or wood, complete a thrower's equipment. The weighed mass of clay is dipped iuto the basin of water, and thrown upon the disc, which is sometimes made of copper, some times of wood. The disc revolves, and the clay, hollowed by the pressure of the thrower's fingers, rises and falls, contracts and expands, according to the velocity of the wheel and the touch of the thrower. When the veasel attains the height indicated by his gauge, and the requisite form, and has been smcothed from ridges within and without by the pressure of yielding fragments of horn or wood, the wheel is checked, and the vessel, severed from the disc by a fine tightly-drawn wire, is removed by an assistant to the drying-room, where it is partially dried previous to being fiaished by the turner.
Turning.—The turner's lathe in maay respects resembles that employed for turning wood or metal. The vessel to be turned is fixed by a small rim of moist clay upon a wooden block, fitting the interior of the vessel, and projecting from a horizontal spindle, to which, motion can be com municated. The tools employed are thin slips of metal or horn, and a polisher consisting of a piece of Parian ware ; sometimes a metallic profile is used, and pressed against the revolving vessel. The turner reduces the superfluous substance of the vessel, and fiaishes the exterior, the bottom, and the rim ; he also, when necessary, polishes the surface. After turning, the ware is replaced in
the drying-room, previous to being fitted with bandies, spouts, or applied decoration. Before removal, however, the internal form of small open ware, as, for instance, cups, is corrected by pressure upon a wooden cone.
Drying.—The drying-room, to which reference has been made, was originally a 10-ft. brick chamber, with a, central stove, and shelves upon the walls for the reception of wure. For the placing and removal of ware, boys had to be repeatedly entering this chamber, a practice which was both laborious and unhealthy. Many contrivances have been devised to do away with the necessity of entering the drying-room, by causing a movable frame to carry the ware from the entrance of the room through the heat,ed atmosphere, and back to the entrance for removal. The best known drying-apparatus is that invented by Culin Miutou Campbell, and represented in Figs. 114l, 1142. The heat is supplied to the drying-chamber by the waste or exhaust steam from a, steam-engine through the flues V, W, and IC. ln the centre of the chamber, is a vertical axis E, from which, project horizontal arms D, attached below to the collar P, and above, by the sloping rods G, to the collar F ; they carry at their outer ends a circular rack H I, whose outer edge comes within a short distance of the outer wall of the drying-chamber. In this wall is 131) opening, covered by a sliding-door A B, through which the ware can be placed upon or removed from the reek. The rack is made with several shelves one above another, and each shelf is made of two concentric strips of wood, with space between, to facilitate the circulation of the heat. The shelves are divided ioto compartments, by vertical partitions running from top to bottom. The machine moves neatly en its axis, and a touch of the hand will cause it to revolve, and expose one compart ment after another. Fig. 1143 shows another arrangement, in which, pans supporting the ware are loosely suspended, in the same manner as scale-pans,frotu trans vt isc bars fixed to the transverse ference of a large, revolving, dicular wheel. The wheel is wide, and the pans hang be tween its two sides ; the bases of tho pans remain horizontal by force of gravitation during the entire revolution of the wheel.