Is it possible to remove the latent image from exposed film?

[shalom_septimus]

<p>This might be a dumb question, but I've never heard it asked before:</p>

<p>Is there any way to reverse the process that occurs when film is exposed, that can remove the latent image before developing it, such that you wind up with a piece of unexposed film that can then be re-exposed?</p>

<p>Reason I'm asking, I've got somewhere a box of dry plates that are so old they don't even have an expiration date. Tried developing one just to see what would happen, and it came out fogged solid. It was from a sealed box, but a century or so of exposure to cosmic radiation was enough to expose it. (Or else my safelight wasn't as safe as I thought, but these were supposed to be orthochromatic, and the box says ruby light is OK.) So I was wondering, is there something I could soak a plate in, perhaps some sort of reducing agent, that would remove the latent image (which in this case is just fog) so I could re-expose the plate once it's been dried? Or is it a strictly one-way process?</p>

<p>(I suppose I could just fix a plate until it's clear, then re-coat with Ag-Plus or similar, but I'd like to try this first if it's at all possible, just to see if it could be done.)</p>

[john_a5]

<p>Fog and exposure create chemical changes that can't be reversed. I think your last idea would work, although I am not sure you couldn't just scrape the plates with a razor blade to remove the emulsion. You might have to do that anyway after fixing to get them totally clear before recoating them.</p>

[john_shriver]

<p>You could bleach it with a "rehalogentating bleach", but you would wind up with a VERY slow silver chloride emulsion with no color sensitization. (We're talking as slow as contact printing papers like Azo.) Not really a very useful solution. You would have to harden the emulsion first, say with formaldehyde hardener.<br>

By the way, most of these glass plates were rather slow anyways, so the fog isn't likely from cosmic rays. More likely simple oxidation (tarnish), they weren't shipped in an air-tight wrap, and the wrapping paper might have a lot of sulfur in it as well (silver sulfide formed - another tarnish). I noticed that the one box of plates I tried using, only the very center of the plates were any good, they had oxidized from the edge in.</p>

[profhlynnjones]

<p>For practical purposes, no.<br>

Lynn</p>