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  • GLOSSARY AND GENERAL INFORMATION (Pottery, for artists)
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  • Alumina, or Oxide of Aluminium, is one of the most abun- dant of earths. Combined with silica it is the chief constituent of kaolins and China clays. It imparts refractory qualities to clays and is an indispensable ingredient of pure glazes. Pure alumina or calcined Aluminium is a chemical product. Ammonia. A volatile gaseous matter, found in some clays. Alkaline in action. Antimony. A silver-white metallic element, used with other oxides as a colourant or to give opacity in glazes. Arsenic. A non-metallic volatile element, used in glaze making. CLAYS: Lime. (See Calcium.) Tincal. (See Borax.)
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  • EQUIPMENT FOR A SMALL POTTERY OR A SCHOOL
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abstract
  • Alumina, or Oxide of Aluminium, is one of the most abun- dant of earths. Combined with silica it is the chief constituent of kaolins and China clays. It imparts refractory qualities to clays and is an indispensable ingredient of pure glazes. Pure alumina or calcined Aluminium is a chemical product. Ammonia. A volatile gaseous matter, found in some clays. Alkaline in action. Antimony. A silver-white metallic element, used with other oxides as a colourant or to give opacity in glazes. Arsenic. A non-metallic volatile element, used in glaze making. Barytes. A heavy spar used with clays to introduce density and vitrescence. Bauxite. A very aluminous earth, used in preparation of pure alumina and to render clays refractory. Boracic Acid. The natural and, usually, impure prod- uct (boric acid being free from chemicals). Borax. The combined chemical product of soda and boracic acid. Used as a strong flux in glazes. Calcined Bones. The residuum of burned bones, used to stiffen artificial porcelain. Calcined Kaolin. Kaolin after it has been subjected to heat to drive off the water combined with it. Calcium Carbonate (Whiting). Found as a white rock, and ground to pure powder. Used with clays for soft bodies. Gives durability to glazes. Calcium Oxide (Lime). A widely distributed earthy matter. Imparts fusibility to clays, in nearly all of which it is present in varying proportions. Chrome, Oxide of. Used in making greens, browns, and blacks. Stands a high fire. CLAYS: Ball Clay. Blue and black. Very plastic clays. Used with non-plastic materials, such as flint, stone, felspar, or whiting, to form fine earthenwares. Cane and Red Clays. Clays coloured by the presence of ferric oxide, and used extensively for bricks, terra-cotta tiles, and common pottery. China Clay. A yellowish-white, non- vitreous clay, prod- uct of the decomposition of granitic or felspathic rocks. Cornish China clay is exceptionally white, pure, and plastic. It is widely used with China, or Corn- wall stone and calcined bones, to make bone porcelain. Felspar is added to render it vitreous. Mixed with ball clays, pipe clays, flint, and stone, it makes the various classes of earthen and stone wares. Pipe Clay. A very white, smooth clay. Less plastic than ball clays. Much used for making slips, en- gobes, and enamels. Saggar Clays or Fire Clays. Coarse refractory clays strengthened by the addition of grog, used for saggars, fire tiles, and bricks. Cobalt Oxide. The oxide of the steel-grey hard metal. Extremely valuable in pottery, making all shades of blue for under-glaze printing or staining. With iron or copper gives blue-greens. Copper, Oxides of, and Carbonate. - Red, green, and black oxides of copper have been of the utmost value to potters. They are used to produce green, blue, turquoise, red, and crimson. Its extraordinary changes in reducing or oxidizing fires are of the greatest interest to the experimenter. Cornish or China Stone. A rock composed of felspar and quartz. Its vitrification (about 1400 C.) im- parts hardness and density to China clays. It is a valuable constituent of glazes. First known as " moorstone " or " growan." Earthy Colourants. Rarely used in modern commercial pottery, except for salt-glazed jars, crocks, and peasant pottery. Felspar. A fusible rock found almost pure or in combina- tion with potash and soda, the greater the percen- tage of alkalies the more fusible being the spar. It is used to replace more refractory materials in clay and to stiffen glazes. Flint. A pure silica with slight traces of calcium. Found in pebble form on seashores. Calcined and ground to a white powder, it is widely used to impart whiteness and strength to clays. Invaluable for bedding and packing in kilns. Used with the fluxes, lead, borax, potash, and soda, to make glazes and glass. Fluorspar. A combination of fluorine and calcium, more fusible than felspar, and of a white colour, felspar being pink. Galena. Lead sulphide, a highly poisonous material used on " peasant " pottery, giving a soft, yellowish, transparent glaze. Gold. Used in solution for delicate purples and lustres. Gypsum. When calcined gypsum becomes plaster of Paris, these two materials, together with the allied marble, limestone, and alabaster, are widely used in pastes (such as Parian), slips, engobes, and variously to impart fusibility or colour properties to glazes. Iron, Oxides of. Have a wide range of colour, from yellow to purple. They are used to stain glazes and colour bodies. They impart fusibility to clays and are carefully excluded from fine white bodies. Kaolin. A fine, white, very pure, and infusible China clay, almost pure alumina and silica. Chiefly used in the manufacture of porcelain and fine earth- enware. Lead (Oxides and Carbonates of). White Lead, Red Lead, Litharge. Are very widely used as a safe and cheap flux. Poisonous. It cannot be used in those glazes that have to stand a high fire. Lime. (See Calcium.) Lynn Sand. (See Quartz Sand.) Magnesia. A white metallic element present in small quantities in most clays. Manganese. The black and brown oxides of this hard metal are much used to stain slips and bodies, and to colour glazes brown or purple. Marls. Amorphous deposits of lime, sand, and clay, very coarse in texture. Used in making saggars, drain pipes, and similar appliances. Nickel. A hard metallic element, the oxides of which are found useful in preparing blacks, greys, and greens. Nitre or Potassium Nitrate, or Saltpetre. A vitreous and aqueous compound, used in some glazes. Plaster of Paris. (See Gypsum.) Potash. Potassium carbonate or the leached ashes of plants. Used from earliest times as a powerful alkaline flux. Potash, Bichromate of. Used for pinks and crystal- line effects. Poisonous. Quartz or Quartz Sand. Like Lynn or silver sand. This mineral is pure silica and free from lime, al- though the sands may contain some small percentage of iron. Used much like flint for bedding or with alkaline fluxes for the finest glazes. Rutile. Oxide of Titanium. Used variously to im- part a yellow tinge to porcelain, and colour and irregularity to some glazes. Salt. Sodium chloride. Sometimes used in glazes, but best known in connection with salt glazing. It vaporizes at about 1200 C., forming a silicate or hard, thin skin of glaze over the clay. Silica. A hard, colourless crystalline element ; found pure, as in quartz, or in combination with alumina and alkalies, as in all clays. Present in all glazes. Soda. Sodium Carbonate. Product of the decomposi- tion of salts with acids. It is a strong alkaline flux and much used in glaze and glass-making. Silver Sand. (See Quartz.) Tin, Oxide of. Used from the earliest times to impart opacity to glazes. Tincal. (See Borax.) Titanium. (See Rutile.) Whitening. (See Lime.) Zinc, Oxide of. A white metallic oxide ; used to brighten and stabilize glazes and colours.
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