If the spindle be diiven by power, the whole operation can be accomplished at once. The profile (Fig. 1147) is fixed to the end of a movable arm, carried by an upright support screwed to the bench through which the spindle works. The arm and the profile can be adjusted at any required height above the mould, and the profile can be pressed upon the clay as it revolves on the " jigger " head, by the handle shown in the figure. After the plate has been formed, it is removed with the mould to the drying-room, and auother mould is substituted. Figs. 1148, 1149 show another case of a profile for shaping the inside respectively of a simple and an under-cut vessel. In each, a bat of clay is carefully placed inside a plaster mould fixed on a jigger-head. The profile A (Fig. 1148), attached to tbe rod B, counterpoised by the weight D, is controlled by the handle C. The jigger-bead P, turning upon the spindle L, supports an apparatus for fixing the mould M.
By means of screws passing through the blocks G H, and pressing upon the rubbers I, the mould can be placed in any desired position upon the jigger-bead, and eccentrically to the profile. In Fig. 1149, the profile 8 turns upon an axis, and can be forced into the clay, or withdrawn, as required. If tbe jigger be set in motion, and the handle be pressed so that the profile be driven into the clay, the vessel will have on its outside the form of the mould, and on its inside tbe form given by the profile. The mould is made in two pieces, so ss to permit the delivery of the vessel. A machine has been introduced for apply ing an automatic profile to a succession of vessels carried upon a revolving table, (matt vessel being held in a separate mould and jigger head. The moulds for ewers, and other vessels of similar shape, are made in two halves ; hats of clay are skilfully laid in both halves, and adapted to the form by means of a sponge and scraper ; the two halves of the mould are then united (see Fig. 1150) and fast ened by a strap, and the complete mould is placed upon a horizontal wheel moved by hand. The seams formed by the junction of the sides of the two bats of clay in the two halves are scraped down by the workman's thumb, there being free access to the interior both from the top and bottom of the mould. The depressions thus wade are filled up with rolls of plastic clay, and the internal surface is msde perfectly smooth by the application of a moistened sponge. The base of the ewsr is made separately on a mould fixed upon a head, and has a ring of plastic clay placed on its surface, which exactly Ste into the bottom opening of the body of the ewer. The body of the ewer in its mould is placed upon the base, and the junction is made smooth and secure by welding the raised ridge on the base into the internal surface of the body. In forming tureens, and other -deep open vessels (see Fig. 1151), whether round or oval, the bats of clay are adjusted upon a plaster block, covered with coarse flannel, of the form of the interior of Ahe vessel to be prodnced ; upon this block, they are inserted ioto the mould which gives the external form of the vessel. For oval vessels,
specially-constructed jiggers and wheels are required. Their motion is adapted to this purpose by the intro duction of an eccentric.
Burning.—Whett the goods are partially dried, they are trimmed, and when thoroughly dry, are packed in deep round or oval saggers (compare Fire ware) to be burnt. At the bottom of each ssgger, is spread a layer of calcined flint or pure sand, and the goods are packed with the greatest care. For plates, a burnt plate is placed at the bottom, and others are piled upon it. Wide-mouthed and handled wares have burnt rings of the required shape inserted in them, to prevent distortion. The saggers, thus packed, are piled one above another, the interstices being filled by rolls of clay expressed by a small screw-press, until the kiln is full (compare Kilns, p. 1563). The progress of the burning is ascertained by the periodical withdrawal of test-pieces. The firing lasts 48-50 hours. When the firing is cornplete, and the kiln is sufficiently cooled, the saggers are unpacked, and the ware is rubbed over with saud-paper, preparatory to printing or glazing.
Printing.—See section on Decoration, p. 1597.
Glazing. — For the glaze, a mixture of borax, Cornish stone, calcic carbonate, flint, and kaolin, is first fused in a small reverberatory furnace, shown in section in Fig. 1152 : A is the stoke-hole ; M, fire-place ; N, grate ; K, damper ; FI S B, bed on which the mixture rests, having been thrown in at V ; P, chimney ; R, opening by which the mix ture, when thoroughly fused, is run out into an iron vessel containing water. The molten mass is broken up by the cold water, and is transferred to small mills, similar to those employed for grindiog flint and Cornish stone. After prolonged grinding with water, and passing through sieves of great flUOIle1818, it is purified by agitation in a blunger armed with horse-shoe magnets, Figs. 1153,1154 : B is a vertical axis driven from the pulley FI ; C, four arms projecting from the axis ; E, bars fastened by the bolts D to the arms C, and holding the magnets, as shown. A proportion of this slip is mixed with a slip consisting of Cornish stone and plumbic carbonate, or an equivalent of plumbic oxide. Into this liquid mixture contained in convenient tanks, the wares rendered porous by burniog are dipped; the mixture is kept in constant agitation, and the porosity of the ware ensures enough being taken up to produce a sufficient glaze. Considerable skill is required to dip the different forms of ware in such a manner that the glaze may be equally distributed, and as little surface as possible be covered by the dipper's hand. Fig. 1155 shows an arrang,ement, c,onsisting of a thimble with a hook attached, for enabling the dipper to handle with facility plates and other ve•stls of large diameter. When the parts that havo been rubbed, or insufficiently covered with the liquid glaz,e, have been retouched, and the ware has been thoroughly dried, it is replaced in Baggers, preparatory to the fusion of the glaze.