Paixtbej.—The pieces of porcelain or earthenware to be enamelled and enriched by gilding, are, after the first firing, dipped in a suitable glaze, and again submitted to the fire; they are then delivered to the painter or ena meller. The colours used in enamel-painting are composed of metallic calves and fluxes, suitable to each other, separately and conjointly, and of such s nature as to fuse them sufficiently for the glazing on which they are laid. Gold has also its flux, and is laid on as other colours are. When the painting is com pleted, the ware is placed in • furnace less in size, and different in construction, from that before noticed. Care is here necessary in the arrangement of the vessels, and great nicety is required in the degree and the continuation of the heat, which is not so intense as in the former firings. The colours after this firing put on a shining appearance, but the gold has an opaque yellow east, and is burnished with a blood-stone to give it the desired brilliancy.
The deleterious effects of glazes, composed principally of WO, having engaged the attention of the Society of Arts, they were induced to offer their largest honorary premium for the discovery of a glaze for the common red composed of materials not any ways prejudicial to the health, and which, cheapness and fusibility, at the comparatively low temperature required by red pottery, might supersede the use of lead in that branch of manufacture. The following method was communicated to the Society by Mr. Meigh, of Skel ton, for which the Society awarded him the premium :—The vessels are to be first i dipped In a mixture of red marl, ground in water to an impalpable paste, in order to fill up the pores with the fine particles of the marl; the vessels are then glazed with a mixture of the consistence of cream, of equal parts of black manganese, Nlass, and Cornish stone, well ground and mixed together, and when the ware is well dried it is fired as usuaL For • white glaze, the man ganese is omitted.
Owing to the vast extent of the manufacture of refined sugar in this country, there is a very great and constant demand for sugar4oaf moulds, which are a species of unglazed red pottery, made upon the potter's wheel. Masers. T. and R. Powell, of Bristol, however, by an improved patent process, now form them upon a mould, preparatory to turning, and afterwards give them • glaze both inside and out. The machinery employed by the patentees is represented in the following Pip. 1, 2, and 3. a, .l ig. lirsents the mould formed of wood or plaster of Paris, or both, and turned tly smooth ; it has a cylindrical pin 6 in the apex, and in the centre of e base, • hole to receive the head of an upright spindle c, which projects about an inch through the disc d; upon this diac the mould is placed, a small pin from d entering a hole in the base to carry it with the disc, when the spindle (which is placed at the potter's table,) is set in motion by a band passing round the pulley e.
Fig. 2 represents the press in which the clay is prepared for the mould. a a the cheek of the preen ; b, a stout triangular box secured to the sides of the pen, of the shape shown by the dotted hnes.on Fig. 3 ; c, a table supported by hinges at one end, and at the other by wedges resting on the s fiat hoard f, (shown separate to Fay. 3,) is placed upon the table under b; in the box b is a thick plank, of the shape of an interior of f, and across b is placed a stout block of wood g, which is retained in its place by iron straps h bolted to b, and having forelock's passing through the top of them ; in g works the screw k, its upper end being steadied by the cross-piece 1, and the lower end pressing upon the thick plank in b.
.Fig. 3 represents the plank f, which is half an inch thick, and having a piece taken out of the centre (as shown in the figure); the dotted lines represent the exterior shape of 6, the interior being the same as f. The operation is as fol lows: the plank f being placed on the table and elided under b, the table is wedged up, and the forelocks are withdrawn from the straps k; the block g and screw k are raised by a rope ; the box b is then to be filled with clay, and covered with the thick plank before mentioned; g is then replaced, and the forelocks driven in : the screw being now turned, presses the clay into the mould plank f; a wire is then drawn through between the plank f and the box b; the wedges being knocked out, the plank/ is withdrawn, and replaced by another, and the table again wedged up. The piece of clay in f is then to be removed, andupon the mould Fig. 1, round which it is wrapped, the edges closed together, andthen turned fair and smooth: it is afterwards removed, when suffi ciently dry, to the kiln; and when burnt enough, the salt glaze is given in the usual manner. Instead of the box b, a number of planks like f may be placed upon each other, and being firmly clamped together, the clay may be pressed into them by the screw, and then being undamped, a wire may be paned be tween each, which thus gives the clay ready for the turning mould.