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Origins of Glass
Origins of glass, history of glass, all about glass are not known as they are lost in history,.
It is known that the Romans first used a glass like material for ornaments, beads, bottles and in Pompei was found a cast of crude glass 3 by 4 feet (800 by 1100 mm) in size.
By the tenth century A.D. the Venetian island of Murano had become the known world’s center of glassmaking, producing crown glass and cylinder glass for windows. Both the crown and cylinder processes began by blowing a large glass sphere. In the crown process, the heated glass sphere was adhered to an iron rod called a punty opposite the blowpipe.
The blowpipe was then removed, leaving a hole opposite the punty. Next, the sphere was reheated, whereupon the glassworker spun the punty rapidly, causing centrifugal force to open the sphere into a large disk, or crown, 30 inches (750 mm) or more in diameter. When the crown was cut into panes, one pane always contained the “bullseye” where the punty was attached before being cracked off.
In the cylinder process, the sphere, heated to a molten state, was swung back and forth, pendulum fashion, on the end of the blowpipe to elongate it into a cylinder. The hemispherical ends were cut off and the remaining cylinder was slit lengthwise, reheated, opened and flattened into a rectangular sheet of glass that was later cut into panes of any desired size.
Prior to the introduction of modern glass making techniques, crown glass was favored over cylinder glass for its surface finish, which was smooth and brilliant because it was formed without contacting another material. Cylinder glass, though more economical to produce, was limited in surface by quality by the texture and cleanliness of the surface on which it was flattened.
Neither crown glass or cylinder glass was of such optical quality for the fine mirrors desired by the 17th century nobility. For this reason, plate glass was first produced, in France in the late 17th century. Molten glass was cast into frames, spread into sheets by rollers, cooled, then ground flat and polished with abrasives, first on one side and then the other. The result was a costly glass of near perfect optical quality in sheets of unusual large size.
Mechanization of the grinding and polishing operations in the 19th century reduced the price of plate glass to a level that allowed it to be used for storefronts in both Europe and America.
In the 19th century, the cylinder process evolved into a method of drawing cylinders of molten glass vertically from a crucible. This made possible the routine, economical production of cylinders 40 to 50 feet (12-15 m) long. In 1851 the Crystal Palace in London was glazed with 900,000 square feet (84,000 square meters) of cylinder glass supported on a cast iron frame.
In the early years of the 20th century cylinder glass production was gradually replaced by processes that pulled flat sheets of drawn glass directly from a container of molten glass. Highly mechanized production lines for the grinding and polishing of plate glass were established, with rough glass sheets entering the line continuously at one end and finished sheets emerging at the other.
In 1959, the English firm of Pilkington Brothers Ltd started production of float glass, which has since been licensed to other glassmakers and has become the worldwide standard, replacing both drawn glass and plate glass. In this process, a ribbon of molten glass is floated across a bath of molten tin, where it hardens before touching a solid surface.
The resulting sheets of glass have a parallel surfaces, high opitical quality and a brilliant surface finish. Float glass has been produced in America since 1963 and now accounts for nearly all of domestic flat glass production.
Origins of Glass Origins of Glass
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