Theorically speaking: yes, but since all the silver compounds which were unnecessary to the image had been already removed with a fixer, and those which actually form the image had already been exposed, the image structure won't change anymore when exposed to light. But it may change, to some extent, its apparent density or colour depending on the developing / toning agent you use. That's why you can do all toning works in daylight.
Originally Posted by Sparky
But again: before attempting any chemical work, take a look around on this forum. Please note how many problems (spots, casts...) people have to deal with even with brand new, perfectly fixed and well washed papers. Just imagine what may happen with an old, dirty, probably not well fixed and even less washed photograph, which has reacted over years with hundreds of unknown aggressive compounds which usually fill the air. As Donald said, FORGET that what appears as a corroded spot on the picture, will show any detail if toned.
The increase of contrast you can have with a digital expansion of dynamic will kick you out of the window. Try it.
I know a chap who does excellent portraits. The chap is a camera.
(Tristan Tzara, 1922)
Well, permanganate isn't (in and of itself) a rehalogenating bleach. Ferricycanide, as usually used in solutions like Farmer's Reducer, is, but the bleaches that include sulfuric acid are not.
But yes, if bleached with a rehalogenating bleach, the silver halide that results is light sensitive and must be either light fogged or chemically fogged in order to redevelop (note that the thiocarbamide solution in bleach/redevelop sepia systems is a self-fogging developer, sort of). This property can be used for situations like recovering the color information in C-41 film accidentally developed as B&W -- bleach with rehalogenating bleach (like non-fixing C-41 bleach), fog, and then develop as normal in C-41, and the dye couplers that B&W process doesn't remove will allow the color dyes to set and the negatives to convert to color negatives.
Conversely, a halogenating bleach used to reduce an image must be fixed to preventing printing out from long term light exposure, while sulfuric acid based bleaches completely remove the bleached silver and require no further treatment beyond the sodium sulfite clearing bath, if removing the silver image is all that's required.
Photography has always fascinated me -- as a child, simply for the magic of capturing an image onto glossy paper with a little box, but as an adult because of the unique juxtaposition of science and art -- the physics of optics, the mechanics of the camera, the chemistry of film and developer, alongside the art in seeing, composing, exposing, processing and printing.
I highly recommend that you purchase a copy of "Conservation of Photographs", Eastman Kodak Company, ISBN 0-87985-352-2, cat 193 5725. I think you will find chapter 8 "Deterioration" and chapter 11 "Restoration of Deteriorated Images" on point. The approach of the book is that you first need to test the image to determine the type of deterioration (they give very good examples) and then you treat the deterioration by a specific means. It also lays out all the pit falls of attempting the different types of restoration. If the pitfalls don't scare you off from trying the restoration, their instructions will save you from re-inventing the wheel.
It is also a good read on how to process and store your current images for maximum longevity.
From an old clipping in my collection :
" To restore old stained and faded prints : soak the print for 10 minutes in a 1% solution of formalin. Stain the print in a dilute solution of potassium permanganate or pot.bichromate,then wash. Bleach the print to whiteness in a 10% solution of sodium bisulfite and wash again. Develop the print in any print developer under a bright light to the desired density then fix and wash as normal. According to the book, this treatment will restore beautifully any old b&w photograph."
Just wanted to thank you for your rational, knowledgeable and considered responses... I am inspired. Though this will be a few months down the road... and Smudger (!) - what the heck... that sounds pretty authoratative - and PERHAPS crazy enough to work. Can't hurt to try...! And it would be FUN huffing the formalin, too! Might preserve me somewhat as a side bonus.
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Do you remember what the source was for that BTW??
The clipping quoted was from a book called "Tricks for Camera Owners", published in 1939. I have no other info but it's likely an American publication,given the spelling of bisulfite..(Anglophones use the bisulphite variation).
Originally Posted by Sparky
The formalin is obviously to harden the emulsion. Another source (Ilford Manual of Photography) suggests potassium alum as an alternative.
I would be interested to know if it works - please post your results.
And - make a copy neg first.
I think Donald Qualls' first reply in this thread was dead-on. You risk losing the images entirely, or further damaging them.
Atmospheric pollution is a major player in fading of albumen prints. You will likely not restore detail in any faded areas. You risk further bleaching away any detail that might be there, information that might well be enhanced digitally.
I scan dozens of old photographs a day for the Oregon Historical Society. Most are silver-gelatin, many are older prints, including albumen prints. By selecting the color channel appropriate for the color of the stain, you can filter out a great deal of visual "clutter" in an image, and by simply adjusting contrast, bring back an amazing amount of hidden detail. I've pulled some incredibly good visual information from photographs that are badly faded, and I use an Epson scanner with SilverFast software, nothing fancy.
Digital imaging is a boon to restoring or just preserving old images. We have no budget or lab facilities for restoring faded images. We preserve as best is possible what we have, and scan them for future reference.
I think the first step is to do no harm. Digital imaging is your friend here. Zero impact, high return. This is salvage work, not creativity.