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I have been carrying out some research on Venetian paperweights for a talk I am giving at the end of the month at the Wheaton Village Paperweight Fest. I don't think it is possible to be certain of the factory: Bigaglia ran a factory making millefiori canes (mainly for beads), but he did make some paperweights using Francini canes as well as simpler canes that may well have been his own. However, there were other glass factories on Murano, and there seems to be little record of what they made. Regarding dates, I think it is most likely mid to late1840s: there were very few made in the rest of the 19th century.
Alan