United States Chinaware

UNITED STATES CHINAWARE Earthenware.—The tableware made in the United States represents to a very large extent a high grade of white earthen ware, also called semi-vitreous or white ware. This product is made in 6o potteries and its composition is approximately as fol lows : English ball clay 13%, feldspar 13, English china clay 25, North Carolina kaolin Io, Florida kaolin 6, flint 33. However, the use of American clays is steadily replacing the imported materials. The biscuit firing is done at about 2,200° F, pyrometric cone 8, the glost firing at 2,150°, cone 5, and the decorating firing at 1,350°, cone .017. The glaze is invariably a boro-silicate of the alkalies, lime, lead and zinc. The operations are practically the same which prevail in Staffordshire (England) except that both the bisque and the glost firing are carried to a higher temperature. The use of tunnel kilns for all three firings has become very ex tensive. Ivory coloured ware is produced in large quantities and this colour is obtained through the use of larger amounts of Ameri can ball clay and the introduction of yellowish firing kaolins. The tendency towards the application of vivid overglaze colours is very marked at the present time. Practically no under-glaze deco ration is applied. The principal centre of the white earthenware industry is East Liverpool, 0., including potteries located just across the Ohio river, at Newell and Chester, W. Va. Within a short distance of East Liverpool factories are operating at Sebring, East Palestine, Salineville, Minerva and Carrollton, 0. Formerly, a considerable quantity of white ware was produced at Trenton, N.J. But this activity has diminished to comparatively small operations.

Vitreous Ware.

The demand for non-absorbent, vitreous table ware for hotels and restaurants has stimulated the American potters to develop such a product quite obviously from the semi vitreous type of body through the increase in fluxing material and the raising of the bisque firing temperature. Thus, the composi tion of a vitreous body would be as follows: Feldspar 15%, flint 38, ball clay 6, china clay or kaolin 4o, whiting 1. The biscuit firing is carried to cone 11, or about 2,300° F. The resulting product shows the "stony" type of vitrification as distinguished from the "glassy" structure, possesses great toughness and mechanical strength and is translucent but markedly less so than the hard fire porcelains of continental Europe and bone china. The proc esses are essentially the same as practised in the earthenware manufacture except that, previous to the biscuit firing, the green flat ware is sanded, in which operation sand is shaken between the individual plates of a bung. The glaze is practically the same as that of earthenware though it is fired to a somewhat higher tem perature. Under-glaze decoration is used to a large extent though largely confined to lines and plain printing. However, increased application is being made of polychrome lithographic transfer, decalcomania, as the development of the industry extends to the production of household china. Over-glaze decoration is also applied. The vitreous tableware industry is scattered and fac tories are located at Trenton, N.J., Syracuse, N.Y., Beaver Falls, Pa., New Castle, Pa., Wheeling and Clarksburg, W.Va., and Wellsville, 0.

Belleek China.

There is produced in the United States a highly decorated grade of china, known as the Belleek type, which is named after a similar porcelain produced in Ireland. This pro duct has attained an international reputation under the name of Lenox china. The porcelain is highly translucent, of an ivory colour and has a texture well suited for ornate decoration. The main flux of the body is a pre-fused, glassy mass, composed of feldspar, flint and alkalies. The body thus consists of this flux, feldspar, china and ball clay. The biscuit firing temperature is con siderably below the maturing point of the other types of porce lain. The glaze is a very brilliant boro-silicate of the alkalies, lime, lead and zinc. The principal production of this type of china is at Trenton, N.J.

Hard Fire China.—Hard fire china, similar to the porcelains of Austria, Czechoslovakia, France and Germany, with a low temperature biscuit and high glost fire, is produced only by three factories and on a comparatively small scale. The body employed is somewhat more silicious than the typical European product, which has approximately the composition : Kaolin, 5o%, feldspar, 25% and flint, 25%. The glost firing temperature is somewhat lower than that of European practice, being close to 2,41o° F, or cone 12. There are indications that a considerable expansion in the production of hard fire porcelain is to be looked for in the near future. Laboratory and technical porcelain is being pro duced by two factories.

The subject of high fire porcelain cannot be dismissed without referring to an American development which works with exceed ingly high temperatures. Through the introduction of synthetic mixtures or of natural minerals of the sillimanite group which have the general composition, aluminous porcelains are produced which show remarkable mechanical strength and re sistance to thermal shock. These properties are associated with the extensive development within the fired body, of a crystalline compound, mullite, which has the composition, This compound is formed in all porcelains but in these special bodies, through the deliberate exclusion of nearly all crystalline silica and its replacement by the aluminum silicate just referred to, a very large proportion of the mass consists of mullite. The porce lains are fired at temperatures between 2,650-3,000° F, cones 17 to 3o. The dense crystalline structure and the low thermal ex pansion are responsible for the high mechanical strength and re sistance to thermal shock. This type of porcelain is marketed in the form of insulators for spark plugs and other electrical pur poses, laboratory and technical ware, special refractories, etc. Products of this kind have become known on the market as sillimanite porcelain.

Bone china, as made in England, is produced in the United States only in relatively small quantities, owing to the lack of the specially skilled and trained workers required in its manufac ture. (A. V. B.)