Glass and Glazing

The use of glass in building depends on its method of production.  This determines the size and strength of the sheets.

Early glass for windows was produced by spinning a lump of molten glass on the end of a metal bar to form a disc of thin glass about three feet in diameter.  This was cut into small lozenges or squares which were then joined with cames of lead to form the familiar 'leaded lights' - the piece in the middle of the disc, where it had been broken off from the metal bar.  The 'bull's eye' was used in unimportant windows.  The window frame is usually metal or the leaded light is fixed into carved stone.

Developments also took place in the composition of the glass including potash from burnt wood, possibly as a result of the early glassworks in Chiddingford and other places on the Weald.

Flat glass was later made by forming molten glass into a cylinder which was then opened up. This enabled the Georgians to produce the familiar timber frame sash windows with the glass held by slender mullions, often six panes of glass to a single sash.

Production improvements enabled larger sheets to be made, hence the Victorian windows with only one or two panes of glass per sash.

Later flat glass was produced by pouring it onto a plate hence 'plate glass'.  For a finer finish it was polished.  This led to the shop windows of the late nineteenth century.

'Float glass' developed by Pilkington's in the 1950s is made by floating molten glass on to molten metal with a low melting point.  Recent developments in improving the strength of glass make it possible to use glass as a building material in its own right.