It was a bit of lateral thinking that brought the result, Paul.
The butter dish is in the Useful (as opposed to Ornamental) designs classification. I had a read of the Nat.Arch. helpfile to see what it says about them...
Registers and representations under the 1843 Act 1843-1884
... record series BT 45 and BT 46.
These are the designs submitted to the Patents, Designs and Trade Marks Office under the terms of the Non-ornamental ('Useful') Designs Act 1843. Representations by classification ‘useful’, design range 1-6740.
The registers are divided into three parts: a register of the items by design number, an index to proprietors’ names in BT 46/5-7 and an alphabetical index to subjects in BT 46/9.
01/09/1843 30/06/1884 1-6740 Non-Ornamental (Useful) Designs
Representations: BT 45/1-30
Registers: BT 46/1-4
Index to Proprietors' Names: BT 46/5-7 (7 (8
01/09/1843 12/04/1883- Alphabetic Index to Subjects
BT 46/9 (8
Diamond marks were used on all material classes, i.e.
VII-XIII Textiles of various kinds, including dress and furnishing fabrics
But that doesn't help explain why yours is an oval one! Neil:
If you go to the Nat. Arch. website and into the Discovery catalogue search box put:
"Useful Registered Design Number" glass
and select 1800-1899 as the date range, it brings up 74 registrations, which include two for Manchester Glass - 4631 (as above) and 4632 (another butter dish.) Hope this helps.