Resensitizing exposed glass plates

[Don_ih]

I have slow orthochromatic glass plates that have been exposed to light. I was wondering if there could be a way to resentsitize them. They were already slow. I'm essentially wondering if dev/bleach/clear/dry would work and what kind of bleach (Ferricyanide + pot bromide?).

 

[revdoc]

I would guess that fogging and developing, followed by bleaching in darkness, should work. The results won't be like the original plate... in particular, any sensitisation using sulfur, gold or dyes will be lost. But in theory, it would be a light-sensitive, bromide plate.

Try it, and tell us what happens!

 

[koraks]

I really doubt that a rehalogrnating bleach will yield 'unexposed' silver halides. Maybe try it on a plate, see what happens.

 

[Don_ih]

That did ... nothing.

The plate developed completely. I used potossium ferricyanide and potassium bromide to bleach the plate. I didn't wait for it to dry. I exposed it with a black bottle cap on it, then redeveloped. It slowly fogged all over.

Frankly, while I was doing it, I couldn't see any reason why it would work. I think something more would be needed. The exposed and developed silver is bleached, but all that does is "undevelop" it - it doesn't "unexpose" it (which is what I'd like).

I have a bunch of these plates. I can fix them and put liquid light on them, if I want to bother with them, I guess. I can save that for a time when I can't think of anything whatsoever that's better to do.

 

[lamerko]

Recently I made similar attempts, but on old and very badly weathered negatives. I selected one color Kodak 5296 EXR 500T and one black and white ORWO NP-27 (400 ASA), both of which expired in the early 1990s or more than 30 years ago. Processed normally, both produce a very dense fog, completely useless.
I don't remember if I exposed them to light, I guess not. And that might have been a mistake. I treated it, in standard ferricyanide bleach with sodium bromide, but maybe it should have been ammonium. I wonder if a little chloride would help. After the bleach, I washed them well and doused them in 98% isopropyl alcohol. They dried almost instantly.
The result - ORWO NP-27 was again with massive, extremely dense fog. I should note here that this is a film containing quite of silver.
The big surprise was the EXR 500T - there was no sign of the massive fog. The film mask was extremely clean! But in haste I had set 320 EI. Film sensitivity has dropped quite a bit (since time), maybe somewhere around EI 12-25. I received an extremely thin negative, but for the first time I also saw color from it. I'll have to try again

 

[Don_ih]

I'll have to try again

Sounds promising. Certainly worth trying again.

 

[AnselMortensen]

I remember reading somewhere, a long time ago, that portrait photographers who shot glass plates back in the day would scrape the emulsion off of old plates & recoat them.

 

[Don_ih]

Well, my plates aren't that old. They're Kodak ortho plates made about 60 years ago (yeah, not that old). They've been opened to daylight so they develop out max density. I was stupid enough to buy them. The plate I messed with this morning, developed, bleached, developed, bleached again, developed again - bleached one last time. Every redevelopment (even though exposed to more light), less development occurred. So, I contact printed a leaf on it under a 150 watt bulb for about 2 hours. I dunked it in developer for a few seconds and then fixed it. Very very thin negative. I should have left it longer in the developer. Not sure anything more would have happened, though.

 

[Don_ih]

 

[koraks]

Quite pretty; I like it.

 

[Don_ih]

Quite pretty; I like it.

I would also say "impossible to enlarge". This is one of those things that can be seen by a scanner and virtually disappears when you shine light through it.

Next time, I won't get my thumb- or fingerprint on it. Maybe. The emulsion was pretty soft after being cooked under 150 watts for 2 hours.

 

[Don_ih]

So, what happens? I developed the fully exposed plate, bleached it. When I redeveloped it, it developed more slowly and didn't get as dense as it did before. That was true of the next time, also. The last time I developed the plate, it turned a grey the colour of cigarette ash. Why was it not redeveloping back to fully black?

 

[koraks]

IDK, but it matches experiences I've had from time to time torturing silver halide emulsions with repeated bleaching etc. Once it starts going south for some reason, things get Antarctic pretty badly.