am sure that Ivo and John know more about these wares than me - I got carried away with finding a picture of what seemed a very similar bowl, although it looks to be possible that this piece is attributed to Sowerby. Unfortunately, I can't see the base of the book example so don't know if that is folded or not.
There seems to have been some confusion as to exactly who made some of these pieces - ex Salviati employees who came to the U.K. or made on Murano - certainly it seems that Sowerby "employed for a time a small group of expert glass blowers brought over from Italy". It's worth reading Cottle to realize just how confusing attribution for some of this material seems to have become.
Salviati did have a London shop and as John is saying he may well have sold imported Murano wares only.
Sue, from what I can see of this bowl it doesn't have a folded foot. Plenty of the Venetian Renaissance pieces from the last third of the C19 did have folded feet, and so do many of the pieces made on Murano in the 1950's and '60's - the foot on this bowl looks unusually thick.
If you go on line am sure you will find images of C16 or C17 Venetian pieces with folded feet - the glass is obviously very thin, so folded to strengthen the edge, and the fold is very evident.
