It's opal glass,David's got one I believe,don't think they're rare and it was less than a fiver if I remember.
Yes I have got one. They are not that common, but were not made with opal glass - I think you'll find it was sprayed on the rear. Opal glass only appears to have been used for a very short time for some trays and a very few handkerchief vases.
However, there were two types of opal glass used: solid opal, such as some of the Playing Cards from the mid-1950s - see photo in my book - and are quite scarce. The other is opal-flashed, like Cut Pearl, and some of the earlier trays, like the Vintage Cars. Provisionally, I would date the use of opal-flashed up to about 1962.
"Seeing" the archives (if they let you down into the basement - unlikely) is mind-boggling. You have to make an appointment and request what you wish to see from the archives. Naturally, that's very difficult when you don't know what's available, but there are some employment records. Also, if I do find any mention of your grandfather, I can't tell you if it's documented after 1929 as I've had to sign the Data Protection Act... but I'll hint very broadly
Remember, as I have said before, there is 30 cubic metres of the stuff for me to wade through over the next year or so. I have already taken over 3,000 photos in 9 visits and am currently working on building a device to allow me to photograph both pages of an open ledger (which cannot be flattened!) in one go.
See Laura Brett's blog
: she is the archivist and has done much of the work in reorganising what was shipped down from St Helens.