POTTERY 613 



makes from l,000to 1,200 plates of earthenware in the same time. The pieces, which 

 are not round, are shaped in plaster-moulds, and finished by hand. When the 

 articles are very large, as wash-hand basins, salads, &c., a flat cake is spread above a 

 skin on the marble slab, which is then applied to the mould with the sponge, as for 

 plates ; and they are finished by hand. 



The projecting pieces, such as handles, beaks, spouts, and ornaments, are moulded 

 and adjusted separately ; and are cemented to the bodies of china-ware with slip, or 

 porcelain dough thinned with water. In fact, the mechanical processes with porcelain 

 and the finer stoneware are substantially the same ; only they require more time and 

 greater nicety. The least defect in the fabrication, the smallest bit added, an unequal 

 pressure, the cracks of the moulds, although well repaired, and seemingly effaced in 

 the clay shape, re-appear after it is baked. The articles should be allowed to dry 

 very slowly ; if hurried but a little, they are liable to be spoiled. When quite dry, 

 they are taken to the kiln. 



The kiln for hard porcelain at Sevres is a kind of tower in two flats, constructed 

 of fire-bricks ; and resembles, in other respects, the earthenware kilns already figured 

 and described. The fuel is young aspen wood, very dry, and cleft very small ; it is 

 put into the apertures of the four outside furnaces or fire-mouths, which discharge 

 their flames into the inside of the kiln ; each floor being closed in above, by a dome 

 pierced with holes. The whole is covered in by a roof with an open passage, placed 

 at a proper distance from the uppermost dome. There is, therefore, no chimney proper 

 so called. 



The raw pieces are put into the upper floor of the kiln ; where they receive a heat 

 of about the 60th degree of Wedgwood's pyrometer, and a commencement of baking, 

 which, without altering the shape, or causing a perceptible shrinking of their bulk, 

 makes them completely dry, and gives them suflicient solidity to bear handling. By 

 this preliminary baking, the clay loses its property of forming a paste with water ; and 

 the pieces become fit for receiving the glazing coat, as they may be dipped in water 

 without risk of breakage. 



The glaze of hard porcelain is a felspar rock ; this being ground to a very fine 

 powder, is worked into a paste with water mingled with a little vinegar. All the 

 articles are dipped into this milky liquid for an instant ; and as they are very porous 

 they absorb the water greedily, whereby a layer of the felspar-glaze is deposited on 

 their surface, in a nearly dry state, as soon as they are lifted out. Glaze-pap is 

 afterwards applied with a hair-brush to the projecting edges, or any points where it 

 has not taken ; and the powder is then removed from the part on which the article is 

 to stand, lest it should get fixed to its support in the fire. After these operations, it is 

 replaced in the kiln, to be completely baked. 



The articles are put into saggers, like those of fine stoneware ; and this operation 

 is one of the most delicate and expensive in the manufacture of porcelain. The 

 saggers are made of the plastic or potter's clay of Abondant, to which about a third 

 part of cement of broken saggers has been added. 



As the porcelain pieces soften somewhat in the fire, they cannot be set above each 

 other, even were they free from glaze ; for the same reason they cannot be baked on 

 tripods, several of them being in one case, as is done with stoneware. Every piece of 

 porcelain requires a sagger for itself. They must, moreover, be placed on a perfectly 

 flat surface, because in softening they would be apt to conform to the irregularities of 

 a rough one. When, therefore, any piece, a soup-plate for example, is to be saggered, 

 there is laid on the bottom of the case a perfectly true disc or round cake of stone- 

 ware, made of the sagger material, and it is secured in its place on three small props 

 of a clay-lute consisting of potter's clay mixed with a great deal of sand. When the 

 cake is carefully levelled, it is moistened, and dusted over with sand, or coated with a 

 film of fire-clay slip, and the porcelain is carefully set on it. The sand or fire-clay 

 hinders it from sticking to the cake. Several small articles may be set on the same 

 cake, provided they do not touch one another. 



The saggers containing the pieces thus arranged are piled up in the kiln over each 

 other, in the columnar form, till the whole space be occupied ; leaving very moderate 

 intervals between the columns to favour the draught of the fires. The whole being 

 arranged with these precautions and several others too minute to be specified here,' 

 the door of the kiln is built up with three rows of bricks, leaving merely an opening 

 8 inches square, through which there is access to a sagger with the nearest side cut 

 off. In this sagger are put fragments of porcelain intended to be withdrawn from 

 time to time, in order to judge of the progress of the baking. These are called trial- 

 pieces or watches (montres). This opening into the watches is closed by a stopper of 

 stoneware. 



The firing begins by throwing into the furnace -mouths some pretty large pieces of 

 white wood; and the heat is maintained for about 15 hours, gradually raising it by 



