This is what I am talking about....
Roman mosaic bowl, circa 1st c. AD
The Corning Museum of Glass
This is an example of a Roman or Hellenistic mosaic bowl. It was constructed by preparing canesof glass, long rods with designs layered in them. These canes were sliced into small pieces, revealing the layers of colored glass, and the slices were placed side by side to form the initial shape of the bowl.
Some say the bowl was formed by placing the cane slices into the bottom of a two-part mold, replacing the top of the mold, then firing to fuse the slices.
Other researchers feel that evidence supports the fusing of the cane elements into a flat disk, with the striped rim applied while the glass is hot, then slumping the disk over a convex ceramic form, thus forming the bowl.
Personally, I'm inclined to believe the latter hypothesis. Having worked with cane slices before, I find it difficult to believe that numerous slices would be placed in a mold and would stay securely while the top of the mold was put in place and fired. Those little slices of glass would be moving all over the place, unless some kind of wash or preparation was applied to stick them in place. The problem with that, in my opinion, is that whatever was used to stick them in place could contaminate the work. It seems like a whole lot of effort to go through when a simpler solution is technologically available. It's a much much simpler process to lay the cane flat on a kiln shelf, and fuse the entire thing, then slump it over something to the desired shape. This way, the ribbon edge can be hand-applied in the heat of the kiln while the disk is flat, making it much more uniform.
Here are a couple of other examples of extant bowls:
(all photos taken by me at The Corning Museum of Glass, October 2010)
Similar to the mosaic bowls are what are termed 'ribbon bowls'. They are made form long slices of cane, as opposed to the short chunks as the previous examples. The construction method is the same: sticks of glass are laid side by side, cut to length to make the desired round shape. The disk is fused and the ribbon rim is applied. The disk is then slumped over a mold to make the bowl shape. Here are some examples:
I hope this post has proved informative and interesting. Roman and Hellenistic glass is beautiful, functional, and technologically advanced, and very much worthy of scholarly attention.
Some good resources on the subject include the following:
Roman Glassmakers: http://www.romanglassmakers.co.uk/mosaics.htm
Roman Glass in the Corning Museum of Glass: http://www.amazon.com/Roman-Glass-Corning-Museum-III/dp/0872901556
The Metropolitan Museum of Art: http://www.metmuseum.org/toah/hd/rgls/hd_rgls.htm