crown glass

This method for the manufacture of flat glass had been invented in Germany in the fourth century A.D. The method is as follows (see image):

1. A blob of molten glass is taken from the furnace with a blowpipe.
2. The blob is inflated.
3. The resulting balloon is flattened by pressing it against a flat surface.
4. On the other side of the balloon, a solid iron bar, the "punty" rod, is attached, and the blowpipe removed.
5. The opening is stretched as far as it will go, resulting in some sort of wide bowl.
6. This bowl is swung around rapidly so that it turns into a round, flat disc.
7. The central knob, where the “punty” rod was attached, is cut out, and the remaining flat segments are then cut into lozenges.