Glaze alkaline

Egyptian faience A non-ceramic material made from a mixture of quartz, lime, soda, alumina, and feldspar, which is fired and covered with a layer of usually blue, alkaline glaze. 

Egyptian Blue. A colour resulting from the formation of a complex copper silicate in an alkaline glaze or glass the colour was much used by the ancient Egyptians and subsequently by the Persians. 

First alkaline glazes the middle of the seeond millennium BC... 

This dissociated zircon is amenable to hot aqueous caustic leaching to remove the siHca in the form of soluble sodium siHcate. The remaining skeletal stmcture of zirconia is readily washed to remove residual caustic. Purity of this zirconia is direcdy related to the purity of the starting zircon since only siHca, phosphate, and trace alkaHes and alkaline earth are removed during the leach. This zirconia, and the untreated dissociated zircon, are both proposed for use in ceramic color glazes (36) (see Colorants for ceramics). 

Cobalt(II) phosphate octahydrate [10294-50-5], Co2(P0272 8H20, is a red to purple amorphous powder. The product is obtained by reaction of an alkaline phosphate and solutions of cobalt salts. The material is insoluble in water or alkaU, but dissolves in mineral acids. The phosphate is used in glazes, enamels, pigments (qv) and plastic resins, and in certain steel (qv) phosphating operations (see Enamels,PORCELAIN ORVITREOUS). 

Porcelain apparatus. Porcelain is generally employed for operations in which hot liquids are to remain in contact with the vessel for prolonged periods. It is usually considered to be more resistant to solutions, particularly alkaline solutions, than glass, although this will depend primarily upon the quality of the glaze. Shallow porcelain basins with lips are employed for evaporations. Casseroles are lipped, flat-bottomed porcelain dishes provided with handles they are more convenient to use than dishes. 

Monochrome black, pea-green and white, or white glazes mottled with black were produced using primarily alkaline-based glazes. Only one example of each of these types was also produced using low-lead, alkaline-based glazes. Ceramics in this group date from the Parthian, Sasanian and Islamic Periods. 

It is likely that the low percentages of lead observed in Mesopotamian ceramic glazes result from a technological choice made by potters, rather than an accidental inclusion. The argument for continuity of the use of lead from low-lead, alkaline-based glazes to lead-based glazes would be strengthened if it could be demonstrated that there was also continuity in the source of lead. 

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