Thank you for your suggestion of sugar bowl Christine, I have found some excellent American glass examples from the early 19th century in R. A. Robertsons “Chats on old glass” and I must admit I thought my piece was too deep for a sugar bowl but seeing those it is a possibility.
Notwithstanding your excellent descriptions of a “porringer” Frank and Nigel, a description that I may add is echoed by Wikipedia, I find it fascinating that 98% of all “porringers” illustrated on 2 auction result sites, several reference books and countless antiques valuation books have 2 handles and some 68% of these could hardly be described as having a shallow bowl, indeed one example of a glass “porringer” illustrated in “English Table Glass” by Percy Bate, published 1913, is over 11 inches in height and is similar to this 6 ½ inch one.
http://www.antique-glass.co.uk/Collectors_curiosities.htmSo though my piece is technically not a “porringer” there does seem to be a general acceptance within the antiques arena that a two handled deep cup can be described as a “porringer”.
However, whatever one wants to describe my piece as, it is undeniably a magnificent example of early 19th century glassware. :thup: