On the question of whether the "Venetian ball" was hollow or solid ...I do not know why I said (or implied) earlier that the “Venetian balls” were hollow. I may simply have been mistaken and did not think too hard before posting my comment. However, I may have been strongly influenced some years back by something I read in a book I never purchased, but for which I have recently seen a copy of some relevant pages …
Paperweights, Michael Kovacek, 1987
In his lead-in text discussing the “Genesis of Paperweights” he briefly covers the work of the ancient Egyptians and Romans and goes on to say:
… the first period of Venetian glass-making. One glass ball dates from this time, and this can be considered the ancestor of future paperweights. It is a hollow ball made of millefiori segments with gold leaf applied behind. … This beautiful ball is fitted into a Gothic reliquary, which is at the Fürstlich Hohenzollernsches Museum in Sigmaringen.
… Most probably this hollow millefiori ball is identical with the little balls mentioned by Marc Antonio Sabellico in his “De Situ Urbis Venetae”, written around 1495: “… include in a little ball all the sorts of flowers which clothe the meadows in spring.”
… The question of whether the Venetian glass-makers … of the 19th century … knew these hollow glass balls of the late 15th century … cannot be answered … There is, however a striking similarity between the hollow ball in the Sigmaringen reliquary and the Venetian paperweights.
And from the part of Kovacek’s text that I have seen, which is actually just a general summary of developments from ancient to more modern times, he makes no mention of “Venetian balls” being solid!
So, perhaps I can use Kovacek's text as my excuse? But that would be unkind - the mistake was mine!
What I am sure of, however, is that most of the literary references I have recently reviewed (based on at least 30 books / articles) indicate that the “Venetian ball” was (normally) solid and often drilled through. The drilled hole was probably to provide a means of fitting into an item such as a reliquary or a table / pedestal ornament.
For confirmation, the "Venetian balls", rather than being just a mass of canes smoothed out in some way, all seem to have had an outer layer of clear glass and the final shaping seems to have left the surface quite smooth. This is similar to many modern paperweights that have the decoration set just below the surface of the clear glass - including the so-called "scrambled" weights of Bigaglia & co.
Also, it is interesting that the various authors either make little comment on a clear definition of "Venetian ball" or they point to various types of item as fitting the "conglomerated mass" (as stated by Pellatt). Dates for the "balls" are usually suggested as 15th or 16th or 17th century.
[Some comments on Pellat's book entry and on "letter-weights" to follow]