bung to the .:harge of a kiln. When all this is arranged, the furnaces are lighted, and great care is taken to have the best coal, as it enables the manufacturer to make a more certain calculation as to its effects, and is less liable to smoke and suiphureous vapors, which might injuriously of feet the contents of the kiln. The baking or tiring requires great care and attention, and there are many nice regulations connected with it to guide the workmen. It usually lasts from 40 to 42 hours. The fire is then allowed to go out, and the kiln to cool very gradually, after which it is opened and the seggars removed, to be unpacked in a separate workshop. The articles are now in the state called biscuit-ware, and require both the glaze and any patterns they may be intended to bear. Common pot tery is often figured by printing the design in enamel colors on paper, and whilst the printing is still wet, apply ing it to the biscuit-ware; the ware absorbs the enamel ink, and the paper is removed by water, leaving the pat tern on the ware. It is then fired in seggars, or a muffle, to fix the color, and is then dipped into composition called glaze, of which three kinds are used in the Staffordshire potteries. The first, for common pipe-clay ware, is composed of Cornish granite, 16 parts; flint, 36 parts; white-lead, 53 parts ; and culler, or broken flint glass, 4 parts. These materials are triturated with water, with the same care and by similar means to those employed in forming paste, and are reduced with water to the same milk like liquidity. Each workman has a tub of the glaze before him; and as the articles of biscuit - ware, either with or without decorations, are brought to him, he dips them in the glaze, so as to insure a uniform coating over them; and, by nice management, lie prevents any large drops or accumulations on one part more than another. The porous biscuit-ware rap idly absorbs the moisture, and dries up the thin film of glaze on the surface of the arti cles, which are again placed in seggars, and carried to the glaze-kiln, where they undergo another firing, which melts the glaze, and converts it into a perfectly transpar ent glass, like water, all over the surface, and renders any pattern previously printed upon it very plain. The temperature in the glaze or enamel kiln is only in&eased very gradually, and is kept up for about fourteen hours, after which it is allowed to cool slowly, and the articles are taken out completed. So far, this description has applied to the manufacture of pottery and porcelain on a large scale, for general purposes; but when it is applied to more costly and artistic works, very special arrangements are required: and in the case of remarkably fine pieces, instead of the huge kilns, which hold frequently many thousand pieces, muffle furnaces are both used for the biscuit, the glaze, and the colored and gilded decorations, which, in porcelain, are applied on the glaze, and not on the biscuit.
The decoration of porcelain has held a high rank as a fine art; and the exquisite skill shown in some of the finest works of the continental manufactures, and lately in those of Britain, has fairly entitled it to that rank. The colors employed are all colored glasses ground• to impalpable powders, and mixed with borax or some other fluxing material; for use they are generally made liquid with oil of spike, and they are laid on with hair-pencilS in the same way as oil-colors. The whole process is exactly the same as in painting or staining glass; the glaze on the biscuit-porcelain being true glass, and the enamel colors being exactly the same as those used by the glass decorator. The colors may be made by mixing the materials of which glass is made with the coloring material and the flux, or simply with the already colored glass and the flux. When the former plan is employed, the following are the coloring materials employed: oxide of chromium for green; oxide of iron for red, .brown, violet, gray, and yellow; oxide of uranium for orange, yellow, black; oxide of manganese for violet, brown, black, and purple; oxide of cobalt for blue, gray, and black: oxide of antimony for yellow; oxide of titanium for yellow; oxide of copper for green; suboxide of copper for red; sesqui• oxide of iridium for fine black; protoehromate of iron for brown; chromate of lead for yellow.; chromate of barytes for yellow ; chloride of silver for deepening reds and pur
ples; purple of cassius for ruby and purple. Several of these colors are much increased in brilliancy by the addition of oxide of zinc, which of itself gives no color, and the transparent ones are rendered opaque by the addition of oxide of tin.
Other fluxes besides borax, or borate of soda, are used, as sand, feldspar, boracic acid, miniuni or litharge, salt, saltpeter, potash, and soda. Nothing enriches the appearance of porcelain more than good gilding; for this purpose gold-leaf is rubbed down with oil of turpentine, or pulverulent gold is produced by precipitating a solution of gold in aqua-regia, by the addition of a solution of sulphate of iron. The gold is precipitated as a brown powder, which is washed and dried, and then worked up with one-sixteenth of its weight of oxide of bismuth and oil of turpentine. It is painted on, then fired, and afterwatd burnished. Peculiar and beautiful metallic lusters are produced upon pot tery by precipitated platinum and other means; but it is not within the scope of this article to enter into all the details by which the almost numberless variations are pro duced in the manufacture and decoration of this material. The literature relating to its history is rich in treatises for the guidance of those engaged in the art.
The following are the chief varieties of ceramic materials and their usual composi tion: 1. Si)vres, kaolin, 48 parts; sand (pure white), 48 parts; chalk, 4 parts. At Dresden, kaolin, 62 parts; feldspar, 26 parts; broken biscuit-porcelain, 2 parts. At Berlin, kaolin, 76 parts; feldspar, 24 parts. In England three mixtures are used: For common china, ground flints, 75 parts; calcined bones, 180 parts; china-clay, 40 parts; clay, 70 parts. For fine china, ground flints. 66 parts; calcined bones, 100 parts; china clay, 96 parts; Cornish granite, 80 parts. • Fine, for modeling figures, etc., Lynn sand, 150 parts; calcined bones, 300 parts; china-clay, 100 parts; potash, 107 parts. The glaze requires to be varied for nearly all, so that their fusibility may be greater or less, according to the more or less fusible character of the biscuit ingredients. 2. The composition for this is the same as that for the fine English china, but it is used in a liquid state, so as to be poured into the plaster of Paris molds. It requires very great care in the firing. 3. Earthenware (Fr. Faience, from Fayenza, the name of a place in Italy where it was made; Dutch, Delft, from its having been chiefly made at Delft, in Holland).—Made of various kinds of clay, varying in color from yellow to white, accord ing to the quality required; and more or less of powdered calcined flints are mixed with it to give it body and hardness. Sometimes, as in porous vessels, only clay is used. 4. Stoneware, such as is used for jars, bottles, drain-pipes, etc., is made of several kinds of plastic clay, mixed with felspar and sand, and occasionally a little lime, but the mate• rials vary much in different localities.
In Great Britain the potteries not only supply the home demand, but also export to a greater extent than any oth as in Europe; and so rapid and extensive have been the improvements effected in the last ten years by British potters, that both as a manufae turing and as an artistic country Great Britain now stands foremost. In 1875 the exports of earthen and china ware, parian and porcelain (except red pottery and brown stone ware) amounted in value to £1,745,078. The largest quantities are sent to India, North America, and Australia. In North America, however, the manufacture of pottery is carried on with great activity in Jersey City, Philadelphia, Liverpool (in Ohio), and other places.
Most of the celebrated manufacturers of pottery and porcelain, both at home and abroad, have employed a special mark to distinguish their works, and these are now of considerable importance in enabling us to ascertain the origin of choice specimens.