Thanks for that info. Really interesting. I don't know anything about Venetian glass, but I have just been doing a bit of research about the gold leaf technique. Apparently the murrhine surface applied technique was patented in 1876 (by D'Humy) and by 1880 there were three companies which produced drinking glasses using that or a similar method (but not the encased method - cf.Stevens & Willliams?): D'Humy, Salviati and Powell. Salviati exhibited its murrhine wares at the 1878 Paris exhibition and as a result, its rival (who had a shop just down the road on Regent's Street, London), D'Humy, changed his company name to include Murrhina.
I also know that Salviati did copy ancient wares (like Harry Powell) including Roman glass, to cater for the growing demand in antique venetian glass around the 1870s - 1880s.
So my thoughts now are that it could be a Salviati liqueur glass from about 1880 (or D'HUmy - although apparently almost nothing is known about his work). I don't have any books on Salviati (or any non-British glass really), but would like to start collecting. Do you think 1880 is the right sort of date or were these produced later?