Javier: Anita and I have been having a discussion about pulegoso, bollicine and other bubbles, and so I'm interested in the revival of this thread. I've got a few pieces where the bubbles seem to be what you describe as bubbles in the in-between part (as in the F'lli Toso vase). Do you you know what creates those bubbles and are they there intentionally?
It seems to me that here are two ways of adding bubbles to glass, chemically or physically. Chemically it can be done with gasoline and a number of other substances, including wet wood it seems. Do we have a different name for the process for each chemical we add, or do we use the same name? Is it a different process, bollicine, when the pulegoso is cased, or when a chemical other than gasoline is used? I just checked Venini Catalogue Raisonne, which defines pulegoso as "purposely introducing foreign matter into the mass while molten (sodium bicarbonate or petrol) which burns off under intense heat leaving gas pockets of various dimensions." That seems the most practical and useful definition I've come across.
Physically adding the bubbles, bullicante, seems simpler. At some point in the manufacture, the glass come into contact with metal points that penetrate the surface of the glass. The points are either placed on the marver or are in a type of mould. Adding another layer of glass after this creates the bubbles. The regularity of the bubbles depends upon the the physical layout of the points and the manipulation of the glass after this step.
Imagine if we extended this discussion to bubbles in Scandinavian glass?