Page:The American Cyclopædia (1879) Volume XIII.djvu/816

 792 POTTERY AND PORCELAIN POTTO of France has a dense vitreous body, fusible at a high temperature, with a transparent glaze, containing lead. The composition of old Sevres china may be given as follows : A frit was made of melted saltpetre 22 parts, sea salt 7*2, burnt alum 3*6, soda ash 3*6, gyp- sum 3'6, sand from Fontainebleau 60. This was partially vitrified 'in a calcining furnace, then crushed and lixiviated to remove soluble salts, and afterward ground with millstones under water. The ground paste was then mixed with finely levigated chalk and calcareous rnarl, in the proportion of about 75 parts of frit, 17 of chalk, and 8 of calcareous marl. A glaze or enamel was used composed of litharge 38, burnt sand from Fontainebleau 27, calcined flint 11, subcarbonate of potash 15, and sub- carbonate of soda 9 parts in 100. This pro- cess was replaced at Sevres by that of Bott- ger for hard porcelain in 1765. The greater transparency and softer lead glaze are the dis- tinguishing features of soft or tender from real porcelain. The decoration of porcelain is very similar to that of glass, except that it is always intended to be viewed by reflected and not by transmitted light. All the pig- ments are colored glasses, which acquire their lustre and adhesion to the mass by fusion, and consist of a flux with the addition of a coloring ingredient, generally a metallic oxide ; such tints as will not withstand the action of heat being of course excluded. Yellow may be given by adding oxide of titanium or chro- mate of lead and chromate of baryta. Violet brown and black are produced by various pro- portions of oxide of manganese ; blue gray and black, by oxide of cobalt ; brown, by pro- tochromate of iron ; a beautiful black, by ses- quioxide of iridium ; purple, by purple of Cas- sius ; red, by suboxide of copper; green, by oxide of copper and oxide of chromium. The most refractory colors are: for blue, cobalt ; green, chromi- um ; brown, oxides of iron and manganese; yellow, oxide of tita- nium; black, oxide of uranium. These col- ors may be applied to the biscuit or to the glaze, the silicate of an alkali being used with them for a flux. The material is usually mixed with oil of tur- pentine and applied with a brush. The ware is then placed in a muffle in the manner shown in fig. 27, and raised to a heat sufficient to have the pigment fuse into the surface, but far below that neces- sary to fuse the glaze. See "Wedgwood and his Works," by Eliza Meteyard (London, 1873) ; "Two Centuries of Ceramic Art in Bristol," FIG. 27. Muffle. by Richard Champion (London, 1873); Jacque- mart's "History of the Ceramic Art" (New York, 1875); "Ceramic Art at the Vienna Exhibition," by William P. Blake, U. S. com- missioner (New York, 1875); and "Keramic Art of Japan," by George Ashdown Audsley and James L. Bowes (2 vols. fol., 1875 et seq.}. POTTINGER, Sir Henry, an English statesman, born in Ireland in 1789, died in Malta, March 18, 1856. He went to India as a cadet in 1804, occupied high offices there, and in 1839 was created a baronet for his long services as polit- ical resident and for some time regent in Cutch and Sinde. Being sent as envoy to China, he concerted measures with Admiral Parker for the taking of Amoy (Aug. 26, 27, 1841) and other important places, and concluded the treaty of peace (Aug. 29, 1842) which opened the great ports of China to all nations. He was appointed governor of Hong Kong, and in 1844 privy councillor, and received a pension of 1,500. In 1846-'7 he was governor of Cape Colony, and subsequently of Madras till 1854, when he went home. POTTO (cercoleptes, Illig.), a genus of small car- nivorous mammals, inhabiting tropical Ameri- ca. They resemble the bears in their planti- Common Potto (Cercoleptes caudivolvulus). grade movements, and in their dentition, but differ in other characters ; they seem to form the connecting link between the quadrumana and the plantigrade carnivora. The molars are -f-i-f, small, the anterior two conical, and the others tuberculate with flat crowns, ca- nines short and blunt; muzzle short and rounded ; the eyes large ; the tongue slender, long, and extensile ; tail long, hairy, and pre- hensile ; feet plantigrade, but the five toes are separate, capable of independent motion, am provided with sharp claws; legs short; woolly. The common potto, sometimes call< kinkajou (0. caudivolvulus, Illig.), is about th< size of a cat, but more slender, of a genera yellowish brown, sometimes reddish brown in form and habits it resembles the lemurs, nocturnal and an excellent climber, and us(