Crown glass

Crown glass was the most usual method up to about 1840. Figure 6.5 shows the production process. The glass is blown into a bubble, a rod is stuck to the sphere, and the blowpipe then removed. The pin is spun while the glass is heated and the glass bubble opens up, becoming a circular disc up to 1 m in diameter, which can then be cut into panes. The pane in the middle - the bottle glass - is the lowest grade. These panes with a characteristic circle can still be seen in some old windows. Crown glass has low optical quality, with bubbles, stripes and uneven

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The production of crown glass: (a) the glass is blown into a bubble; (b)an iron rod is fixed to the glass bubble; (c) the blowpipe is removed; (d) the glass bubble opens up after being warmed and rotated; (e) when completely open, the bubble becomes a flat, circular pane of glass; (f) the iron rod is removed. The pane ofglass has a thick edge and centre, but is otherwise clear.

The production of crown glass: (a) the glass is blown into a bubble; (b)an iron rod is fixed to the glass bubble; (c) the blowpipe is removed; (d) the glass bubble opens up after being warmed and rotated; (e) when completely open, the bubble becomes a flat, circular pane of glass; (f) the iron rod is removed. The pane ofglass has a thick edge and centre, but is otherwise clear.

thickness. Today it is only used as decoration, or in panes where trans-lucency is not required.

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