Ol’ Uncle Twee Cat’s Photo Esoterica, Pt. 1:
Are you interested in using old expired Ilford glass plate negatives? No? Oh. Well, I am. When you start trying to do this, you will find that they are surprisingly usable and more abundant than one would expect for a product which hasn’t been produced in about fifty years (the last of them were discontinued in 1973). But how to make good use of them? One method is to remove them from the light-tight packaging which has kept them usable and unexposed for many years and then balance them on the tip of your nose in room light. But this is totally ineffective and gives poor results (in fact, it should be said at the outset that photographic glass plates are sensitive to light and will be ruined if you open them in daylight – many people selling them on the internet seem not to realize this). What, then? What to do?
First of all, if you’ve found this, here’s the page you’re most likely looking for. Otherwise, read on. There is much useful information.
The stated speed ratings are provided in the old Hunter & Driffield standard, conversion tables for which are easily available. You can read about this film speed rating system on Wikipedia here.
Given that this system was superseded almost 100 years ago, and was not used in Ilford’s own literature after the 1930’s, I believe this document to be in the public domain, although I have not found a date of publication in it.