Moulding and Turning. — Tea-cups, saucers, basins, jugs, and such like vessels, receive their first shape from the hands of the thrower, who sits on a stool with a fiat circular wooden wheel before him, moving horizontally on a pivot. This wheel is set in motion by the steam-engine, and the workman can increase or diminish its velocity as there is occasion. Upon the centre of the wheel the operator throws a lump of clay of the required size, and forms it into almost any shape, with the utmost facility ; it is then cut from the wheel by a wire, and taken to be dried, that it may acquire sufficient hardness to fit it for the next operation. By turning, the superfluous parts of the clay are taken off, so as to render the article perfectly smooth, and to give it the exact shape. The lathes on which the vessels are turned are also put in motion by the steam engine, and regulated as to speed by the turner The principle of turning earthenware is very similar to that employed in wood turning. The vessels requiring handles and spouts are taken to the handling room, and those which do not want this appendage, after having attained the requisite hardness, are sent to the oven to be baked. The handles, made on a mould of plaster of Paris, are fixed to the vessel with a liquid mixture of the same material as the vessel itself.
For the formation of various articles manufactured in all potteries, moulds made of plaster of Paris are necessary. The modeller forms the shape of the intended vessel out of a solid lump of clay, which, after receiving his finishing touches, is handed to the person who makes the plaster mould from it. Plates and dishes are made from moulds of this kind, upon which the operator lays a piece of day of the length, breadth, and thickness required ; the mould and clay are then placed upon a wheel turning horizontally on apivot; and the operator keeps peeling round with the left hand, and presses the clay to the shape of the mould with the other. The mould and dish together are then carried into a stove moderately heated, where it remains until sufficiently dried to separate. The plate or dish is then cut even at the edges, and in other respects finished : before they are baked the dishes are laid fiat upon or stone flags, that are quite level, in order that they may remain straight until they go to the oven to be fired. Tureens, vegetable dishes, and such articles, are also made in moulds, but require more time and care, being less simple in their form. Figures, flowers and foliage in bas-relief are also formed sepa rately in moulds, and afterwards affixed to the vessel with diluted clay.
Ifring.—When the ware is ready for firing, it is placed in clay cases, called gars, which vary in size and shape according to the articles placed in them. The saggars are put into an oven, shaped like a bee-hive, with an opening at the top; there is also an opening at the side to admit the saggar, but this is closed before the fire is applied. Each saggar is luted to the other by a roll of
soft fire-clay ; this secures the vessels contained in them from dust, the fumes of the fires, and from the effects of the air when the oven is cooling. The fires which heat the oven are placed round it in proper receptacles, which communicate with the interior of the oven by flues, heating every part equally. This first firing gives a higher degree of heat, and is continued much longer than any successive firing ; when once fired, the article is called biscuit ware. The cream coloured, or queen's ware is now carried to the dipping-house, to receive its glazing ; that which is to be printed blue is taken to the printing-house.
Prinfing.—The design is previously engravers on a copper plate, and laid on a stone to warm. The colour (which has oxide of cobalt for its basis) is mixed with a preparation of oils, to fetch out the impression ; this mixture is smeared over the surface of the plate and again cleaned off; leaving the liquid in the engraving only. The paper used to take off the impression is made expressly for thispurpose; it is damped, laid on the copper plate, and passed between two iron rollers, as in ordinary copper-plate printing. The design, being transferred to the paper, is laid immediately upon the ware, being rubbed on with a flannel. After remaining a short time, the ware is put into a tub of water, and the paper is separated from it by a sponge, leaving the design in the most perfect state.
The ware is then dried, and taken to the oven to be burned; during this opera tion, the oil which has been mixed with the colour in the printing is destroyed, and the oxide of cobalt more firmly attached to the ware ; it is then Glazing —The glaziers differ in their composition in all manufactories ; most, however, have oxide of lead for their beds. The ingredients being mixed with water, and well ground, the glaze is ready for use, in which the vessels are dipped. On drying, which takes place instantly, the water contained in the glaze being absorbed by the porosity of the vowel, it is covered with • fine white powder, of a regular thickness; thus, when fired, becomes vitreous, or assumes a glass-like appearance, and, from its transparency, the blue pattern underneath is rendered perfectly visible. In the last firing, especial care is taken to keep one piece from touching the other, or the whole would fuse into one mass. Great attention is also requisite in the firing, give too much or too little heat, either extreme being injurious : the in this, as io the other firing, draws out trial pieces from the oven, with an iron rod, to ascertain the proper degree of heat.