When I digitized my grandmother Esther’s archive this year, I had maybe 2000 photos to ingest, half of them loose, half in scrapbooks. Many of the black and white photos shot prior to 1920 suffered from silvering, the condition where the dark parts of a photo are obscured by a shiny reflective coating. Age and poor storage are to blame. A black and white photographic image, generally speaking, is metallic silver suspended in a gelatin on some backing (paper, metal, glass). All photos, unfortunately, live on Earth, where the atmosphere is full of water and horseshit: e.g. miscellaneous aerosolized acidic compounds. Over time the water and acids penetrate the gelatin, react with the metallic Ag, and yield Ag+ ions. The electrostatic force draws Ag+ to the surface. Air is also full of roaming electrons, and the Ag+ grabs those electrons and turns back to metallic silver, leaving a little mirror-puddle on the surface. Anything that accelerates this process—heat, humidity, more air, dirtier air—accelerates the silvering.
By experimenting and harvesting good background information from archivist blogs, and thanks to a lot of helpful advice from Samy’s Camera in Hollywood, I’ve come up with three methods of dealing with silvering:
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| Grandma Esther |
1) SCAN & RETOUCH
This is the least effective method, but it works well with photos that are only lightly silvered. It requires a scanner and Photoshop. First scan the photo (the higher resolution the better—I always go to 1200dpi). Then, in Photoshop, under Adjustments...Hue/Saturation, select Global Colors (Master), then raise the saturation to +100. Next select only Cyans, and lower the saturation and lightness to -100. Next select only Blues, and do the same thing. You may have to repeat with the Magentas as well. Then select Global Colors (Master) and lower the saturation to -75 or -85 to return the tone to something like the original flavor of sepia.
The point of this process is to isolate the surface silver, which tends toward the blue/cyan part of the spectrum, and restore it to the dark tone it had before it got oxidized. When a photo is only lightly silvered, the results are fine. The heavier the silvering, however, the more obvious it will be in the processed image that the affected areas have been replaced by a series of black dots.
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| Grand-Aunt Myrtle |
2) REPHOTOGRAPH WITH CROSS-POLARIZATION
This is highly effective and was my go-to method throughout the project. For this you’ll need a copy stand, two lights, polarization gels, a DSLR camera, and a lens with a polarization filter.
My gear list:
• Copy stand: I use an Impact PCSLEDK-110 with dual LED panel light kit ($375 from B&H Video)
• Nikon D810 36.3-megapixel single lens reflex (manufactured 2014-2019; bought used, $590 on eBay)
• Nikon Nikkor AF-S 105mm F2.8G ED VR Nano Micro (autofocus macro lens, $387 on eBay)
• Hoya Alpha II CIR-PL 62mm polarization filter ($50, Samy’s Camera)
• Linear polarizing gel, 6 mil, 19” x 12” ($36 from Kinetic Lighting, Glendale, CA)
Set up the copy stand so that the lights are on opposite sides pointing down at a 45-degree angle. Put polarizing gel over each light (if the gel came with a film on top, be sure to peel it off!). Darken your studio so that the only light comes from your two LED sources. With the camera mounted pointing down at a silvered photo, look through the viewfinder and twist the polarization filter until the silvering disappears.
The big advantage of this method is that it doesn’t so much treat the silvering as defeat it. The mirroring fades to nothing like magic and restores the rich, deep blacks that should have been there instead. The only disadvantage that you’re rephotographing a photograph, with the image passing through the multiple glass layers of a camera lens, which inevitably won’t produce results as sharp as a scanner with its tight focal plane and single layer of glass.
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| Harry Kenney, J.P. Arp, & John F. Gilbert |
3) CLEAN THE ORIGINAL
This may in fact be the best solution, but it’s too laborious for me to use it on the thousands of photos in this collection. If you only have a few photos to restore, though, this could be the ticket. Here’s a blog post by Rita Udina, paper & book conservator, summarizing a paper she wrote with two colleagues about silver mirroring and how it could be eliminated:
https://www.ritaudina.com/en/2018/10/14/silver-mirroring-removal-from-historical-photographs/?unapproved=4085&moderation-hash=c24f161082acde6e23f98fa859a91a1c#comment-4085
From her process description:
A cotton swab impregnated with tetrachloroethylene and a small amount of calcium carbonate is applied to the image layer in circular motions. A few minutes are allowed for the solution to neutralize the eventual acidity of the emulsion. The subsequent removal of the calcium carbonate with another swab with tetrachloroethylene, also eliminates silver mirroring, leaving the gelatin intact. At the same time, most of the mould is also eliminated and the effect of old fingermarks is also significantly reduced.
One of the cleaning components, Calcium Carbonate, is easy to procure (it’s a common health supplement). Tetrachloroethylene (PCE), on the other hand, is an environmental hazard and many toxicology agencies consider it a carcinogen. However, in the comment section of the blog a reader asks if sensor cleaning fluid could be used instead, and Rita says yes: “The solvent is just a vehicle to help the calcium action. As long as the solvent does not swell the gelatine, it should work fine.”
Here’s a list comparing the ingredients of three common cleaning fluids used in photography (information gleaned from their various safety data sheets):
- Eclipse (lens cleaning fluid) = 90-99% methanol, 10-1% ethanol
- Aeroclipse (digital sensor cleaning fluid) = 94-95% 1,1,2,2-Tetrafluoroethyl 2,2,2-Trifluoroethyl Ether, 5-6% unknown (trade secret)
- PEC-12 (stain/marking/debris remover for silver-based photo emulsions) = 75-90% ethanol, 10-25% N-Butyl acetate
Eclipse is about $12.49/oz, Aeroclipse about $31.58/oz, and PEC-12 about $5.50/oz (pricing via eBay vendor clubsixteen). I decided to buy some PEC-12. On a clean surface I mixed a few drops of PEC-12 with a dusting of Calcium Carbonate to make a wet paste. I used this to scrub a photograph gently. Then I took a cotton rag daubed with PEC-12 and wiped the photo from edge to edge to remove the residue. This seemed to produce good results.
Restoring a photographic original by cleaning it, assuming it was effective, would of course be the best technique, since you’re curing the issue and not just treating it. However it’s the most dangerous, too, because you run the risk of destroying something unique. Luckily in my grandmother’s collection I often found up to five prints made from the same negative, so if I lost a Mario, I still had more guys left. Practice on photos you don’t need!
