Architectural glass

Architectural glass is glass that is used as a building material. It is most typically used as transparent glazing material in the building envelope, including windows in the external walls. Glass is also used for internal partitions and as an architectural feature. When used in buildings, glass is often of a safety type, which include reinforced, toughened and laminated glasses.

Cast glass windows, albeit with poor optical qualities, began to appear in the most important buildings in Rome and the most luxurious villas of Herculaneum and Pompeii.

One of the earliest methods of glass window manufacture was the crown glass method. Hot blown glass was cut open opposite the pipe, then rapidly spun on a table before it could cool. Centrifugal force shaped the hot globe of glass into a round, flat sheet. The sheet would then be broken off the pipe and trimmed to form a rectangular window to fit into a frame.

At the center of a piece of crown glass, a thick remnant of the original blown bottle neck would remain, hence the name "bullseye." Optical distortions produced by the bullseye could be reduced by grinding the glass. The development of diaper latticed windows was in part because three regular diamond-shaped panes could be conveniently cut from a piece of Crown glass, with minimum waste and with minimum distortion.

This method for manufacturing flat glass panels was very expensive and could not be used to make large panes. It was replaced in the 19th century by the cylinder, sheet, and rolled plate processes, but it is still used in traditional construction and restoration.

In this manufacturing process, glass is blown into a cylindrical iron mould. The ends are cut off and a cut is made down the side of the cylinder. The cut cylinder is then placed in an oven where the cylinder unrolls into a flat glass sheet.

Drawn Sheet glass was made by dipping a leader into a vat of molten glass then pulling that leader straight up while a film of glass hardened just out of the vat – this is known as the Fourcault process. This film or ribbon was pulled up continuously held by tractors on both edges while it cooled. After 12 metres or so it was cut off the vertical ribbon and tipped down to be further cut. This glass is clear but has thickness variations due to small temperature changes just out of the vat as it was hardening. These variations cause lines of slight distortions. This glass may still be seen in older houses. Float glass replaced this process.

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Wikipedia