In reproducing a human figure, or group of figures, every limb is cast singly in a separate mould, and the whole is built up piece by piece, and cemented together in the green state by the interposition of liquid slip. Each mould is in two pieces, fitting closely together, and fixed by projections ou one side protruding into corresponding depressions on the other. An opening is left in the middle of the upper part of the junction of the two sides, through which the liquid mixture can be instilled from a suitable vessel. The cavity of the united mould is filled and re filled as the water is absorbed, aud until a sufficient thickness of paste has been deposited. So soon as the paste has become solid by absorption, the moulds readily deliver. The wares are burnt in specially-prepared saggers, and are supported in every direction by carefully arranged props made of refractory clay. The drapery of figures naay be reproduced by spreading lace, or scree fine textile, upon a slab of plaster, covering it with a layer of liquid paste, wrapping as required upon the figure, and simultaneously solidifying the paste and destroying the fabric by the fire to which the figure is exposed.
The creamy tint of English Parian is due to the formation in the body of the ware of a glass fused in an oxidizing atmosphere, and tinted by the ferric oxide naturally incorporated with the constituent materials. Foreign Pariau has generally a greyish tint, owing to the reductive atmo sphere of the kilns in which it is fired. The name of Belleek is commonly given to a species of glazed and lustred Parian, but the genuine ware is made from a mixture of kaolin and felspar artificially prepared from red orthoclase granite, and which has the property of assuming when fired a natural enamel or egg-shell film.
Artificial Porous Ware.—Porous ware is required for several purposes, especially for water coolers and the inner cells of galvanic batteries. The principle upon which this manufacture is based is the introduction into the clay mixture of a proportion of some organic substance which will be destroyed by heat. The substance generally used is saw-dust. As the battery-cells are required to be exceedingly regular and thin, they are formed by the process of absorption or " casting" which has been already described (compare Parian). A clay containing an appreciable quantity of calcie oxide is unsuited for the manufacture of battery-cells. The moulds employed in the process of casting have constantly to be replaced, as they are subject to damage, by reason of the repeated absorption and evaporation of large quantities of moisture.
English Chince.—English china is generally of a dead or creamy-white colour, is translucent, and is apparently less cold to the touch than hard porcelain. The glaze is soft, and the ware will not resist extreme variations of temperature. The mixture for English china is manipulated and Bred with greater facility and certainty than would be possible with simple granitic materials, and the resultant ware is adapted to a greater range and brilliancy of decoration than is applicable to a harder and less manageable composition. The materials employed are China-clay, or kaolin, ball-clay, Cornish stone, flint, and cakie phosphate, together with, in some cases, a small proportion of steatite, which consists of 63 silica, 33 magnesic oxide, and 4 water. The translucency of English china is due to the fusion of the felspar contained in the Cornish stone. The calcie phos phate performs many useful functions. In addition to reducing shrinkage, and enhancing the whiteness of the ware, it enables it by its infusibility to stand the fire requisite for the vitrification of the felspar, and adds lightness without materially affecting tranalneency. An analysis of a
sample of Worcester china gives : silica, 38.88; alumina, 21.48; calcic oxide, 10.06 ; sodie and potassio oxides, 2.14 ; ealeio phosphate, 26.44. Every manufactory has a different mixture for china, but tho following may be taken as an average specimen : kaolin, 31.00 ; Cornish etone, 26.00 ; calcie phosphate, 40.50; flint, 2.50. The glaze is comported of a fused glass, ground and added to a mixture of Cornish atone, or felspar and plumbic carbonate. A glaze for a body com posed as deaeribed might consist of 60 parts of a glass formed of—Cornish stone, 4S ; borax, 24 ; oalcic carbonate, 20 ; potassic nitrate, 4 ; and sand, 4; added to plumbic carbonate, 16; and Corniah stone, 24.
In selecting materials both for the body and the glaze, the greatest attention is paid to their purity, and freedom from iron.
The processes employed in preparing the materiala and manipulating the pasta are similar to those already described under the head of Earthan-ware (p. 1573), but carried out oo a smaller scale. The plastic clays are broken up by agitation with water, and the Cornish stone, calcio phosphate, and flint are ground with water under etone runner& The grinding-pans measure 10 ft. in diameter and 3 ft. in depth, and are paved with email blocks of chert-stone. The different materials, suspended in water, are eifted, and run by measure into a large receptacle, in which they are mixed and kopt iu agitation by revolving arms, carrying magnets, which attract and withdravr from the mixture any particles of metallic iron that may be present. The mixture is theoca pumped into a filter-press, which is generally of a lighter and simpler construction than that used for earthen-ware. Preasure is applied by a hand pump, and ,the sacks are connected by central fittinga, which, when united, form a siogle central tube through the entire series of' sacks. When the paste is taken from the sacks, it is subjected to repeated beating, turniog, and kneading, before it is conaidered to be in a proper working eondition.
Another method of procedure is to dry the liquid materiala separately by evaporation on a long shallow atone reservoir heated from beneath, and to mix the separate ingredients in the dry state by weight, to remix them with water, theo to pump the liquid mixture first through e Bailee of sieves, next through a aerieti of atationary electro-magneta, and finally into the filter-prese. The ingredienta of the glasa, whioh forms the largest constituent of the glaze, are mixed and in troduced into the furnace represented in Fig. 1152. When melted, it ia run from the furnace into water, broken up, dried, ground, and mixed by weight with the plumbic) carbonate nad ground Coruiah stone. The mixture is then grouud with water in a mill similar to, but smaller than, that uaed for grinding the hard ingredients of the body, until such time as the liquid glaze will pass a silk lawn containing 4000 mulles in 1 sq. in. The ovens and saggers are similar to them used for earthen-ware. The wares are bedded in the saggers in calcined flint, and the saggers are built up in airtight columna by the insertion of rolla of moist clay. The kiln for biscuit-firing takes 40-50 hours to fire, and about 48 hours to cool ; the glaze-kiln takes 15-20 hours to fire, and about 36 hours to cool, and to allow the glaze to become annealed.