The second and most interesting method is to create a new glass pane after a proper modelling, each piece one by one. This second production technique  is used in the typical Venetian "rulli" or "rui" and it is a very ancient technique. Just as an example, a picture of this kind of glass pane refers it as dated to the sixth or seventh century .
The method is very similar to the one used to produce crown glass , but it is used to create singular small panes (about 15 cm diameter) instead of a big sheet of glass to be cut in regular pieces with a grozing iron.
How to model a "rullo veneziano"?
From the video, it is evident a certain attention to the edge, but its cross section is obviously invisible. If the edge bends, it is supposed to bend in the direction of the pontil mark, because it would be the most comfortable direction according to the position of the glass-maker when creating the rondel.
However, in case a proper section of such kind of glass becomes available, and if a close up is needed (remember that the edge is covered by the lead!) the cross section should be shaped accordingly.
half section of the genuine rondel (grid = 1 mm)
|fig. 5 |
3D model of the rondel with pontil mark in evidence (grid = 1 mm)
|fig. 6 |
3D model of the rondel on the opposite side (grid = 1 mm)
8. production of a rondel at Lamberts -
9. production of a crown glass, as shown in Alan Macfarlane Youtube channel -