Page 39 - Curriculum Visions Dynamic Book

One of the results of this scientific revolution was that the cost of glass fell dramatically, and so it could be bought and used by more and more people.
The next stage in the scientific revolution had to wait a century until it was possible to understand the atomic structure of glass. Following the work of W. H. Zachariasen, it was possible for the first time to understand that glass is a solid with disordered atoms.
Crown glass
Making clear, flat glass proved to be one
of the most difficult things to achieve
either by hand or by machine. From
Roman times until the 17th century flat
glass was made by pouring it over a flat
surface and rolling it flat while it was still
in a plastic state. But this still did not produce glass that was of even thickness. After the dangerous act of rolling, the glass was allowed to cool but still had to be ground by hand.
There was another way to make flat glass, known as crown glass. To make it, the glassmaker blew the glass into a bubble that had cylindrical sides. A rod was then attached to the bubble, and the rod and bubble spun quickly. That caused the bubble to change shape into a flat piece of glass. As part of this process, the centre of the bubble collapsed down to a cone-shape. We now call these pieces bull’s-eyes. To save wastage, they could be used for the occasional window pane even though it was impossible to see clearly through the bull’s-eye. Today, bull’s-eyes are made specially for their decorative effect.
The crown method did not produce very large pieces of glass, which is one reason small windows appeared with many glazing bars holding them in place. Again, a difficulty was turned into an advantage through the beautifully proportioned Georgian window frames that made best use of the glass sizes available.
(Above) Spinning a bubble
of glass to make crown glass. The bull’s-eye is seen as the place where the disk attached to the rod.
(Below) This coloured bulls-eye has been used decoratively in a stained-glass window.
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