Fairly longtime reader, delurking with a rather vague question.

I have my great-grandfather's 9x12 Bergheil; it was his "quick grab" camera that rode around in the trunk of the car---as far as he was concerned *real* work was 8x10 and contact prints, full stop, but like anybody else he needed a snapshot camera. I've been shooting 9x12 film and occasionally rollfilm with it, but just took the plunge to buy an old box of plates from a large, well-known auction site. They're Eisenberger Flavirid plates, about which I can find no information anywhere; the box says they're orthochromatic, 26 degrees, which I assume is the same old DIN scale as for film, hence ASA 320 (I think).

That seems pretty fast for plates, so I'm hoping they're relatively recent and haven't had too many years of cosmic rays to fog them. (On the other hand, if they were *that* recent, wouldn't they be panchromatic?) The box has been partially opened at one end, but the black paper wrapping inside seems never to have been broken, so I'm hoping for the best, but I won't be heartbroken if they turn out to be exposed.

So, first off, does anyone know how old these plates are, who this hitherto unknown manufacturer was, and so on? Any idea how protective I should expect the black wrapper to be? Any guesses about which side the emulsion will be on?

My vague plan is to develop a first trial plate by inspection in HC-110. What have other people shooting old plates used as a development protocol?

Thanks in advance (for this and for all the useful information I've leeched off this site over the last couple of years).