Wasn't Sowerby a pressed glass maker? ...
Yes, they were. Cottle tells us that in 1852, when they moved to a 5Β½ acre (2ΒΌ hectare) site in East Street Gateshead to expand, they had six ten-pot furnaces, all under one roof, operating on three shifts per day. By the following year there was a branch of the Glass Cutters Union established in Gateshead. By the 1860s they had eight furnaces and were employing over 450 people, up to over 700 by 1882. They made every type of glass with the possible exception of English Rock Crystal and Cameo. Their output was immense. There was a major shift to pressed glass in the 1860s, but they still made blown glass in some quantity. Decorating by cutting, engraving, and etching was used on pressed, mould blown, and free-blown pieces, both plain blanks and partly mould-decorated items.
It was the same story in Manchester and Sunderland. By comparison the Stourbridge factories were tiny, insignificant glassworks, forced to specialise in the finest quality work simply because they could not compete with the economies of scale of the giant northern factories on mainstream production.
I suggest you read Cottle. Be prepared to be amazed by the numbers. For example in 1883 Sowerby's average output was about 150 tons/tonnes (170 US "short" tons of 2000 lbs) of finished goods per week, none of it bottles or window glass.
One more example of their amazing skills. Cottle discovered that they were making "Clutha" style aesthetic art glass for almost three years before Dresser's designs were made by James Couper & Sons. Indeed Dresser sold Sowerby's art glass at his shop in London. Sowerby exhibited 700 examples of this glass at the 1882 Manchester Art and Industrial Exhibition, followed by 2000 examples put on public display in Newcastle, almost within sight of their glassworks. Yet all this glass is sold today as Clutha by Dresser, ignoring Cottle's revelations, whereas possibly most of it was made by Sowerby, and genuine pieces made by Couper should really be thought of as just copies of Sowerby's art glass, that is if anyone could tell the difference.
That's all, as I am on the verge of trampling all over Simon Cottle's IP rights, and I don't want to be zapped by a moderator. :angel:
Back to topic β it is more likely that Leni's decanters were made in Manchester or Gateshead than Stourbridge, simply by virtue of the relative size and production capacity of the respective glassworks. Publishing the known Manchester pattern books, of which there are a fair number, would be a great help.