Early Glass Production and Window Design
By the 17th Century two main methods where being used to produce glass sheets.
1. Crown glass for the highest quality could be thinner but small panes.
The glass is blown then the bulb cut and spun so the glass flattens and thins out with centrifugal force.
It's normally thinner at the edges, thicker in the middle with the “bulls eye” at the centre.
2. Cylinder glass was lower optical quality, thicker but the sheets could be bigger.
A bulb is blown then elongated by swinging it to a sausage shape. The ends are cut off to make a cylinder that is cut along its length and flattened to make a sheet.
Windows where constructed from these small panes in the same way as church stained glass. Lead “cames” hold the sheets together. The panels are then fitted in stone or timber surrounds. Larger windows have thick mullions and transoms dividing and supporting the panels.
When these where opening casements, the leaded glass was supported by a wrought iron frame and hinged inwards and latter outwards.
Glazing in a 17th century stone mullion window
That’s the basics of British window design for about 1000 years, from the most spectacular cathedrals to country mansions and Inns.