Pete — like you, I've never seen this before. What a marvellous discovery.
Some details:
Naturalistic bouquet:-
I am certain that the worn naturalistic bouquet is a standard Johnson Matthey transfer, and sold by JM eiither off the shelf or as an exclusive deal. All the Davidson, Sowerby and Bagley examples I have seen I have never seen elsewhere, so must have been the subject of world-wide exclusive deals between Johnson Matthey and the respective glassworks. The earliest date I've worked out for such JM / Davidson transfers is early 1950s.
Alternate panels frosted:-
Not common at all on Davidson pieces. I can recall seeing it, just the once, on a 278 vase, the flared vase on a square foot. If it is sharp, ie you can use it as a nail file, it was sandblasted; if smooth, acid-matted.
Banding:-
The decoration on your tumbler is called banding. While I am sure the decoration on both your pieces was done by hand, machine-assisted banding was the norm for large-scale production. There is a good piece on banding in
Pyrex,
60 Years of Design, Tyne & Wear County Council, 1983. This work dates Pyrex banding quite positively to the late 1930s, not post-war, but banding on other glass is popularly held to be an early post-war style, so it may not help with dating.
Note that I haven't checked the transfers with my reference photographs (which I can't find at present), so I can't be completely certain if the transfer was a Davidson exclusive. This is not as daft as it might appear, as evidence I've accumulated over the years shows that all British glassworks helped each other out occasionally, so a short decoration run could have been done by one of the other three, Sowerby, Jobling or Bagley. Hopefully someone can clear this up (or I might find my photographs).
Bernard C.
