Topic: Sowerby Opalescent (blanc de lat) small “gathering apples” 1882

[flying free]

Actually I've just checked the price list of the Venetian on page 440 and there isn't a butter or salt in the list.
Perhaps they might have been their 'finger cups'?  10cm probably isn't that small diameter in reality and perhaps would have functioned as a finger rinser?

It also seems that the range 'Venetian' applies to the style rather than the green with blue because they say the 'Venetian' range is available in 'Flint' or 'Venetian green with turquoise tops'.  So it's the handblown range/style that is called 'Venetian'.  Not specifically green with turquoise rims.  This is probably already known info, but I'd always assumed 'Sowerby Venetian' referred specifically to the blown glass range in green with turquoise applied rims.

[MHT]

Well I have just tried and I can get my delicate (not) fingers in them, so we will call them finger rinsers.

Yes, Venetian is the style, available in flint and green although flint versions are rarer so maybe not so popular.
If you look at the pattern book page in the webpage there are two clear patterns shown and one of the glass jugs in the gallery is in clear flint glass.

[flying free]

If the pair you own are Sowerby Venetian Finger cups in the green with turqoise rim then they were extremely expensive compared to their other finger cups - the most expensive by a long way.  See page 427 of the linked report.
They cost 18 shillings per dozen versus their 'coloured' ones which were 6 shillings per dozen.  Even the ones which were cut flutes and star were only 14 shillings per dozen.