Porcelain, hard-paste

Soft-paste porcelain Hard-paste pcacelain Tin-glazed ware Jasperware Stoneware... 

Hard Porcelain. True feldspathic porcelain (continental porcelain). Hard-paste Porcelain being the older term still used by collectors. The combined nomenclature (q.v.) defines hard porcelain as made from kaolin or kaolinitic clays, quartz, feldspar and sometimes calcium carbonate. It is covered with a colourless transparent glaze fired with the body. See porcelain. 

Chinese hard paste porcelain consisted of kaolin in a pure and very finely divided state, and petuntze (finely ground felspathic stone) and the glaze was made from selected petuntze mixed with specially prepared lime. 

FIGURE 2.4 The flow of ceramic history illustrates the mainstreams of earthenware, terra cotta, and stoneware, of triaxial hard-paste porcelain, of quartz-based bodies, and of tin-glazed ware. Some important shaping and decorative techniques are illustrated, but the diagram is far from complete. 

Bone China has a similar recipe to hard-paste porcelain, but with the addition of 50% animal bone ash (calcium phosphate). This formulation improves strength, translucency, and whiteness of the product and was perfected by Josiah Spode at the end of the eighteenth century. It was then known as English China or Spode China. ... 

Continental Porcelain. The true, feldspathic, hard-paste porcelain (q.v.) made in Western Europe. 

Hard Metals. Intermetaliic carbides, particularly cemented carbides (q.v.) used as cutting tools and abrasives. Hard-paste. See hard porcelain. 

Hard-paste porcelains are obtained from mixtures made up almost exclusively of kaolin, quartz and feldspars. A little chalk (= 2% of the mass) can be added to favor the formation of the viscous liquid. This mixture is very similar to the one used to prepare fine earthenware. It differs from it only because of the almost exclusive use of kaolin as clay and the proportions of the various components. 

Hard-paste porcelains ate particularly used in the field of crockeiy (Limoges porcelain) and as technical ceramics (insulators). 

Figure 4.8. Temperature influence on the shrinkage speed of a hard-paste porcelain, a bone china and a vitreous china...

Foreign Porcelain or China Is tho finest and moat valuable description of ware, distinguished from other wares by the composition of the paste from which it is formed, giving a body of a fine, hard, translucent texture. Great cure is exercised in tho selection of the materials to give a colorless mass after firing. Two essentially... 

Combustion Rate of Carbon—Eq (12-18) can hardly be expected to hold at ignition temperatures. Indeed it is doubtful whether it will hold at temperatures much above 400 deg C even in the case of anthracite coal. Above this point the carbon ignites and a completely new set of conditions pertains to the problem. Studies on the combustion rate of carbon particles have been studied in considerable detail by several investigators. The general method used was described by Parker and Hottel (1936). The device used consists of a furnace in which is suspended a cylindrical rod of carbon 2.5 cm in diameter with a hemispherical end. The rod is mounted on a porcelain tube and suspended from one arm of a balance so that the hemispherical end is downward in the furnace. In this way loss of weight is easily determined. The surface of the specimen is also capable of measurement. Known volumes of air heated to the required temperatures are then made to flow past the carbon, and by means of a small quartz sampling-tube (which can be adjusted at any distance from the specimen) samples are withdrawn for analysis. In this way samples of air may -be analyzed for the amount of carbon dioxide and oxygen present at any distance from the heated particle-surface. 

If the feldspar and quartz content is increased over that in hard porcelain, soft porcelain is obtained which is fired at 100 to 150°C lower temperatures. Highly plastic clay (ball clay) is added to obtain plastic and easy to work pastes, despite the lower kaolin content. Sanitary porcelains for the manufacture of bathroom articles are soft porcelain articles. 

In this section, the effects of chemical strengthening using ion exchange by paste method on the hardness and fracture toughness of dental porcelains with different microstmctures are shown. Table 1 shows descriptions of five porcelain powders used in this study, two recommended to be used as veneering materials for alumina cores (V and Ob) and three recommended for porcelain fused-to-metal restorations (C, D, and B), containing wide variation of leucite fraction (0 to 22 vol%). 

Soft-paste or Fritted Porcelain. A type of porcelain made from a soft body containing a glassy frit and fired at a comparatively low temperature (1100°C). The most famous soft-paste ware was that produced in the 18th century at the Sevres factory in France, and at Chelsea, Derby, Bow, Worcester and Longton Hall in England. The COMBINED nomenclature (q.v.) States that soft porcelain contains less alumina but more silica and fluxes than hard porcelain. See porcelain. 

The porcelains thus obtained are characterized by a vitrified paste which contains generally high mullite concentrations in microciystals, mullite being derived from the high temperature treatment of kaolin. All these components (glass, microcrystals, bubbles) gave the much desired translucidity and hardness. 

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