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Glass (Hard brittle transparent)

a hard, brittle, transparent substance, formed by fusing fusing together together mixtures of the silicates of potash, soda, lime, magnesia, alumina, and lead in various proportions, according to the quality or kind of glass required. Flint glass is used in making table ware and many articles of domestic furniture and fittings. Crown and flint glass are combined in the manufacture of achromatic lenses.

Plate glass is made by pouring it upon a table which has a marginal edge of a height equal to that designed for the thickness of the glass. A roller travels over the table, on the ledges, and flattening out the glass, which is thus made of equal thickness throughout.

Toughened glass is made by heating till it is about to soften, and then plunging it into a bath of oil at a greatly lower temperature. Usually, a mixture chiefly of oily substances, such as oils, tallow, wax, resin, and the like, is put in the bath; and some manufacturers who worked the process for a time dropped the newly made glass vessels, while still hot, into the oleaginous mixture, by which plan neither reheating nor anneal ing by the ordinary process is required.

After the articles acquire the temperature of the bath, they are removed. temperaturstuallych Painted or stained glass is of two styles, enamel and mosaic glass. In enamel glass proper, certain fusible pigments are painted on a sheet of white glass, which is then fired, and the result is a picture the tints of which even in the high lights are not wholly transparent. A modification of this method produces its picture partly by enameling on white glass partly by the use of potmetal glass, the color of which is heightened or modified by the use of enamels. Mosaic glass is made from a design wherein the drawing is given and the colors indicated, which is the working drawing of the glass painted. From this working drawing a kind of map is made are GLASS which gives the various pieces of the mosaic. The glazier cuts these pieces out from sheets of glass of various colors, and hands them back to the painter, who proceeds first to paint the leading lines with a solid opaque enamel, the coloring matter of which is an oxide of iron. This being done the pieces of glass stuck together temporarily (by means of wax) on a glass easel, and the painter slightly shades his bold traced lines with the same opaque color; using sometimes washes, and sometimes hatching of lightly laid-on lines, as in a black and white drawing on paper. Sometimes both washes and hatching are used, and the washed shadows are stippled. In any case the object of the method of shading is to keep the shadows as clear, and to dull the glass as little as the explanation or expression of the subject will admit of. Two or three or more firings are necessary during the process of this painting. This being done, the glass goes back to the glazier's bench again, and he leads it up, and the window, after having been solidified by a stiff cement or putty rubbed into the leaf of the leads, has then only to be put in its place and strengthened by the due iron stay bars.

Of the origin of glass manufacture nothing is known, but according to Egyptologists, the Egyptians made sham jewels of glass at least 5000 or 6000 в. c.

In some of the most ancient tombs scarabs of glass have been found imitating rubies, emeralds, sapphires, and other precious stones. It is probable that the great center of the glass industry of medieval and more recent times, Venice, received its early impulse and lessons from Constantinople. The art began there with the beginning of the city in the 7th century A. D., and there was a marked improvement after the conquest of Constantinople in 1204, and in 1291 the establishments were removed to the island of Murano, the manufacturers forming a guild with a register of nobility and guarding their secret with the greatest jealousy. In 1436 their color glass came into note, and continued so till the close of the century; and in the 16th century lace patterns and mirrors were introduced. In the 15th and 16th centuries plain glass with tasteful ornaments in gilt and enamel; in the 16th, crackled lace and reticulated glass; and in the 17th century, variegated or marbled glasses were produced.

The Venetian glass enjoyed for a long time the monopoly of commerce, and within recent years there has been a marked revival of the skill and enterprise of Venetian craftsmen. In Germany the oldest glass dates from the GLASSITES 16th century, and consists of goblets and tankards of white color, enameled with colored coats of arms and other devices, millefiori, and schmeltz glass. Engraved glass was first introduced by Casper Lehmann, at Prague, in 1609, under imperial protection, and continued by his pupil Schwanhard; and ruby glass by Kunckel in 1679. Glass is said to have been made in 1294 at Quinquengrone, in Normandy, and a common kind was made later in Dauphiné and Provence. In 1665 20 Venetian glass workers were brought by Colbert to Paris, where they set up the blowing of glass and the silvering of mirrors, the famous mirror hall in Versailles having been furnished by them. In 1688 an exclusive privilege of making large plates of glass by casting was conferred on Abraham Thevart. The name Thevart was assumed by a syndicate of capitalists formed to develop and work the invention of Louis Lucas de Nehon, who was the real inventor of plate glass and the founder of the Gobain works, one of the most extensive plate glass works in the world. In France oxide of lead flint glass was made at St. Cloud in 1784; another manufactory was subsequently established at St. Louis in 1790; and the St. Cloud establishment was removed to the vicinity of Mont Cenis, where it flourished till 1827.

It is uncertain whether glass was made in England before the 16th century, as that mentioned may have been imported from Flanders or Venice. In 644 Benedict Biscop introduced makers of glass windows into Northumbria; but window glass was not in general use for windows till the 15th century. Attempts were made to establish glass works at Jamestown, Va., in 1608-1622; at Salem, Mass., in 1639-1640; in New York City before 1664; and in Pennsylvania before 1683. Subsequently works were established in 1780 at Temple, N. H.; in 1792 at Boston; and in 1797 at Pittsburgh.

Plate glass was first made there in 1853, and it is also made at Baltimore and New York. Pressed glass was invented in the United States.