Saturday, 23 August 2008

Crown Glass

Crown glass: The earliest style of glass window

The earliest method 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 forced the hot globe of glass into a round, flat sheet. The sheet would then be broken off the pipe and cut into small sheets.  

This glass could be made coloured and used for stained glass windows, but is typically associated with small paned windows of 16th and 17th century houses. The concentric, curving ripples are characteristic of this process.

At the center of a piece of crown glass, a thick remnant of the original blown bottle neck would remain. They are known as bull's eyes and are feature of late 19th century domestic lead lighting and are sometimes used with cathedral glass or quarry glass in church windows of that date. Optical distortions produced by the bullseye could be reduced by grinding the glass. The development of diamond pane windows was in part due to the fact that three regular diaper 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.