M Pl>TTKHY AND PORCELAIN, MANUFACTURE OF. 



POTTERY AND PORCELAIN, MANUFACTURE OF. 602 



; immediately behind him u the stove-room, in which th.- 

 mould* are ranged on nhclvc*. All being ready, the plate-maker cuU 

 hi* cUy into lengths with a win, and tears off a piece which he bait 

 tut tktt upon hu block by a utroke or two of his batter, or plaster- 

 nMlhrt and polishes the surface by pressing the tide of a long smooth 

 knife acroai it During thu process, which occupies but a few seconds, 

 the boy ha* brought a mould, placed it ' upon the whirler, and taken 

 hi* place at the handle of the jigger. The man places the clay upon 

 the in.inld. and as it whirls, preme it down cloae with his hand ; a 

 profile, or earthenware tool which gires the form to the bottom of the 

 plate, U imoml upon it a* it revolve*, the superfluous clay being cut 

 off by a wire ; the boy instantly catches hold of the mould thus covered 

 with a coating of clay, runs with it to the stove, places it on a Khrlf to 

 dry, and returns with an empty mould ; by which time his master has 

 his clay prepared for another plate. When sufficiently hardened, 

 the bottom of the plate is polished; and when taken off the 

 mould, the edge* are smoothed and polished with moist leather. 

 Cupm, saucers, and hand-basins are now made by this process, instead 

 of being thrown and turned as formerly. By this means they are 

 supplied at a cheaper rate ; one man and a boy being able to manu- 

 facture the articles which by the old mode requires the work of three 

 men and three females. 



Casting is resorted to when a mould is so intricate as to be difficult 

 for the workmen to fill by pressing. Slip clay is poured into the 

 mould, which rapidly absorbs the water, and a coating of clay is de- 

 posited upon the inside ; the remaining fluid U then poured out or 

 drawn with a syringe, and a thicker mixture is put in, and left rather 

 longer than the first before it is withdrawn. The mould is then put 

 into a stove to dry. Goods 4hus made are very light. 



When completed by the workman, the goods are placed on boards to 

 dry, before going to the biscuit-oven, in which they receive the first 

 fire. The details of the process are described in the article already 

 cited ; and the ware, now in the state of bitcuit, a ready for the blue- 

 printer or for the artist, according to its quality and intended 

 appearance. 



In the old days, before the expeditious and cheapening process of 

 clectrotyping was known, a set of engraved plates for a table-service 

 commonly cost ISO/, or 150i ; and would, with proper care, print 2000 

 dozen services before it wanted reciitting. The ink used in printing is 

 made of linseed-oil, boiled with litharge, rosin, balsam of sulphur, or 

 Barbadoes tar ; almost every printer has his favourite recipe for making 

 this tenacious oil, which is the vehicle of the colour to be used. /Hue 

 colour is made of oxide of cobalt, mingled with flint or carbonate of 

 lime BO u to dilute it to the proper tint. Lilac, of smalts 2 parts, man- 

 ganese 1. Brown, zaffre 2, litharge 2. antimony 1, manganese 1. Red- 

 brown, manganese 12, litharge 2, flint 2, glass 1, borax 1. Orange, 

 litharge 6, antimony 4, oxide of tin 1, oxide of iron 2. Pink, sub- 

 chromate of tin and carbonate of lime, equal parts. Green, oxide of 

 chromium, the tints varied with cobalt or tin. /Hack, red-lead 60, 

 antimony 25, manganese 15, fritted together; then add oxide of cobalt 

 40, oxide of tin 5. 



Some patterns ore executed on biscuit by painters, who lay on the 

 colours in gum-water, in which case the firing in the inutile is not 

 required ; but the choice of colours in this kind of painting is rather 

 limited, as the heat of the glazing-oven and the chemical action 

 of the materials of the glaze would be destructive to many colours 

 which are used by the enameller upon the glaze. For a descrip- 

 tion of the modes of printing and glazing, see EAUTHKXWAKK. 

 The following glazes are excellent, and have been successfully 

 used in the Staffordshire potteries ; they must be ground very fine at 

 the mill. Cream-colour glaze. White-lead 66, Cornish granite 22, 

 flint 12. Prinled-tcare ','aze. White-lead 45, Cornish granite 28, flint 

 13, flint-glass 14. In these forms, the ingredients are simply ground 

 together, and are therefore called raw glazes, in distinction from 

 such as have a portion of the materials first united by calcination into 

 a frit, or incipient glass ; by this practice, a more complete combination 

 is effected, a thinner coating of glaze will suffice, and the ware in con- 

 sequence is loss liable to craze with change of temperature. Prilled 

 glaze. Cornish granite 80, flint 16, red-lead 25, soda 12, borax 17; 

 mix and calcine in the easiest part of the gloss-oven, in saggers lined 

 with flint; then take of the frit 20, Cornish granite 15, flint-glass 10, 

 flint 1>, white-lead 40 ; grind the whole with a little oxide of cobalt, to 

 increase the whiteness. Drab-wart glaze, Litharge 56, Cornish granite 

 20, flint 24. flint glaze. f]int, 40, borax 24, red-lead 16, Cornish 

 granite 7, sofla 5, oxide of tin 5, oxide of cobalt 5 ; calcine, then grind 

 with the addition of a little pearl-ash. Green glaze. Dissolve six 

 pounds of sulphate of copper, and precipitate it with a solution of 

 borax ; to which add 10 quart? of white glaze. Yellow glaze. Colour 

 white glace with king's yellow, to the depth of tint desired; or chro- 

 mate of lead. Black gtate. Red-lead 74, flint 14, manganese 10, pro- 

 toxide of iron 2. 



We proceed to point out the chief differences between tarthcxirare 

 and porcelain. 



Porttlai* a a finer specie* of ware, in which the ingredients are so 

 elected that they act chemically upon each other, and are brought to 

 a state of vitrification. The fracture has n dense or greasy surface, 

 like that of a flint stone, nnd is not li.il.ln to be acted upon by 

 a :ids. When the porcelain U coloured by metallic matter, it is called 



tloitt-trarr ; jasper and .some drab-ware are of this description ; but 

 when it U perfectly free from colouring matter, and is transl 

 it is called CAimi .- f which there are two species, fianl and tuft. 

 It U necessary to bear in miml. lio\\e\cr, t<i prevent confusion, that 

 many writers treat porrelai* and rAinn u convertible terms, applying 

 tli.' former name u well u the Utter to translucent ware only. 



Hard china is made of rilex, generally a fine sea-sand, kaolin or 

 china-clay, and felspar ; sometime* the felspar is omitted, and a small 

 quantity of selenite, or carbonate of barytes, or strontian, is used in its 

 place. 



//cm/ tVima body is made of kaolin 70, felspar 14, sand 12, K. 

 4. The mixture is sometimes nude in lime-water, and must be 

 ground very fine at a mill. When the paste is moulded into the 

 desired forms, it is fired in the biscuit-oven at a moderate heat; 

 when taken out, it is very bibulous, and opaque. In this state it is 

 dipped in the glaze, which is felspar, ground fine, with the addition of 

 a little alkali. Some prefer a mixture of felspar and broken china 

 ground together. It in then submitted to a second fire of great 

 intensity, which not only mrlU the glaze on the surface, but vitrifies 

 the entire mass, which thus unites with the softer matter on tli. j Mir- 

 face so completely, that the glaze does not form a coating of glass 

 upon the body, but appears like the surface of a stone polished by a 

 lapidary. This homogeneity prevents any crazing ; but the process is 

 one of much hazard, for if the fire is prolonged beyond the critical 

 moment when the vitrification is effected, and the surface has 1>< 

 bright, the goods will melt, and sink in the saggers. Oriental, French, 

 and German china are made on this principle ; but the English 

 followed the safer practice which we shall next describe, and which the 

 French manufacturers, aware of its advantages, now adopt. >WV in- 

 Tender China is made by firing the biscuit to iU full vitrescence in the 

 first oven, the shape of the articles being preserved, during their vitres- 

 cence, by being imbedded in flint-powder, Ac. ; and then glazing in 

 the second oven at a lower degree of heat, so as not to endanger the 

 melting of the goods. The union between the body and the glaze is 

 however more complete than in earthenware, the glazing-fire 

 much more intense. Bones calcined and ground are largely used in 

 the manufacture of English china, combined with aluminous and 

 silicious earths in such proportions that they will vitrify together. 

 This effect is promoted by the phosphoric acid of the bones, which at 

 a high heat diffuses itself through all the materials, and unites 

 them into a translucent enamel, less apt to sink and lose its form 

 than the hard porcelain ; it therefore may be Aiade in larger ovens, 

 and with less risk of loss to the potter. EnglixH China body consists of 

 bone 46, china clay 31 , Cornish granite 23. For large pieces, such as 

 dishes, &c., a little Dorset clay is added, to give more ductility in 

 working and more stability iu the fire ; but when great purity of 

 whiteness and transparency are wanted, a higher degree of vitrescenco 

 is obtained by fritting silex and bone together as the basis of the body. 

 China body comprises bone 55, Lynn sand 27, potash 2, cal- 

 cined together ; then ground fine, with China clay 18. (A 

 is harder than for earthenware. Tho following is excellent: 

 Cornish granite 25, soda 6, borax 3, nitre 1 ; mix, and frit in gloss- 

 oven; then take frit 26, Cornish granite 26, white-lead 81, flint ", 

 carbonate of lime 7, oxide of tin 3. The whiteness is increased by 

 the addition pf a little oxide of cobalt. Another China glaze consists 

 of felspar 38, Lynn sand 24, carbonate of lime 11, borax 27 : to be 

 fritted ; then take frit 60, Cornish granite 20, white-lead 20. 



The application of the glaze and mode of firing are the same as 

 already described. 



The decoration of china by enamel colours and gold affords 

 employment to a great number of persona, some of whom attain 

 great excellence in their art. The colours used are all prepared 

 from metallic oxides, which arc ground with fluxes, or fusible glasses, 

 of various degrees of softness, suited to the peculiar colours with 

 which they ore used. The flux of most general application is made of 

 red-lead 6, borax 4, flint 2. When painted, the goods are placed in 

 the enamel-kiln, where the fluxed colours melt, and fasten to the 

 glazed surface. The judicious management of these mixtures 

 requires much study, and is still susceptible of improvement by 

 the aid of chemical science, /liar* are made from cobalt, varied 

 by the addition of the oxides of zinc or tin. Phosphoric acid 

 gives it a rich purple tint; alumina also varies its hue. Green is 

 from oxide of copper, melted with a soft flux, and ground ; its tints 

 are varied by adding blue or yellow or white enamel. Fine greens, 

 which bear a fire that destroys n copper-green, are mode from pro- 

 toxide of chrome, varied with the addition of cobalt, lead, tin, or 

 alumina. Red consist* of nitrate of iron, dichromato of lead, or 

 muriate of manganese. Pink, of subchromate of tin. Rote-colour, of 

 gold and tin (precipitate of oassius) with a little silver. Brown, of 

 ohromate of iron or antimony, lead, and manganese. Orange, of anti- 

 mony, tin, and iron. YeVotr, of antimony, tin, and lead ; also 

 chromste of lead. Marl; of oxide of platinum or iron, cobalt, nickel, 

 and antimony. HVnVr, of arsenic and tin. An infinite variety 01 

 may be obtained by a skilful combination of the above with suitable 

 fluxes, the description of which in detail would exceed our limit-. 

 Ken- potters prepare their own colours; they are supplied )>y persons 

 who devote themselves to that art. 



Cold is applied to china in the i-tato of amalgam ground fine in tur- 



