Crystal Glass, which is a silicate of lead and potash, is made from best sand 100 parts, red lead 66 parts, potash carbonate 33 parts, cullet 50 parts, to which a small proportion of potash nitre, arsenic, and manganese dioxide is added. The bulk of English cut-glass table ware and fancy goods are made from this type of glass. It gives very brilliant and colourless results, more especially when cut and polished. A second-rate quality of crystal glass for table ware may consist of a silicate of lead and soda, as follows: sand 100 parts, red lead 66 parts, soda carbonate 25 parts, cullet 50 parts; with small proportions of Chili nitre, arsenic, and manganese.
Bohemian Glass is made from sand 100 parts, potash carbonate 35 parts, lime carbonate 15 parts, cullet 50 parts; with small proportions of potash nitre, arsenic, and manganese dioxide. This type of glass is used mostly by continental manufacturers for chemical ware, table and mirror glass. It is a hard, brilliant, and stable glass, very suitable for enamelled glassware. It is a silicate of potash and lime.
Pressed Glass consists of sand 100 parts, soda carbonate 50 parts, barium carbonate 15 parts, cullet 50 parts; together with soda nitre, arsenic, manganese, and cobalt. This is used by manufacturers of pressed glass table ware or moulded ware. It is a silicate of soda and barium, the barium having a direct influence in giving a good surface to the pressed goods.
Crown Glass consists of a silicate of soda and lime; sand 100 parts, soda carbonate 36 parts, lime carbonate 24 parts, soda sulphate 12 parts, cullet 50 parts; with traces of manganese and cobalt. This glass is used for making sheet window glass by the crown, disc, and cylinder methods.
Plate Glass is a silicate of soda and lime; sand 100 parts, soda sulphate 55 parts, limestone 30 parts, coal or anthracite 5 parts; with traces of nickel oxide, cobalt, or antimony oxide. This is used for cast plate glass, rolled plate, cathedral glass, window and mirror glass.
The Complex Glasses may be described as those in which more than three bases are introduced, and constitute such types of glasswares as bottles, thermometer tubes, chemical ware, etc.
Common Bottle Glass may be described as an example of complex formulae. Common bottle glass, or tank metal, is made from a silicate of soda, alumina, lime, magnesia, and iron, as follows: Common sand, containing iron and alumina, 100 parts; greenstone or basalt (a silicate of alumina, iron, lime, magnesia, and potash), 25 parts; dolomite limestone (magnesia and lime), 30 parts; sulphate of soda, 35 parts; carbon, 5 parts. Felspathic granites may be also used in such glasses.
Bottle glasses require intense heat to melt, and are usually dark in colour when made from igneous rocks, owing to the large amount of colorific oxides present in such materials. These dark colours are not objected to in bottles for stout, wine, and beer.
It will be noticed these formulae cover a long range, from the best table glass to the commonest dark bottle glass. Besides these, opal, opalescent, and fancy glasses are made, in which either arsenic, tin, alumina, antimony, zinc or barium oxides or borates phosphates and fluorides may enter into the compositions.
Glass makers’ recipes vary considerably in the proportions of the various materials used, according to the locality and the type of furnace used. Generally, it will be found that, where a gas-fired furnace is in use, a larger proportion of sand can be used and a cheaper metal produced.