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Eliminating silver tarnish from antique silver pictures (daguerreotypes)

I am interested in removing tarnish from a silver picture (daguerreotype). These were the first commercially available pictures in the 1850s. The mirror polished silver plated copper was exposed to iodine [affil links] fumes. This created a layer of silver iodide. The plate was then exposed to an image as we would a negative today. Then the plate was held over a pool of mercury heated to 75 C. The mercury vapor would form an amalgam with the silver. The amalgam creates an image. To finish, the plate was washed in sodium thiosulphate ⇦ this on eBay or Amazon [affil links] then treated with gold chloride. Because the target surface was large and the silver iodide density was high, the details are breath-taking. Under enough magnification you can discern the patterns of an iris in an inch high head! I remember some old chemist telling me some salt like sodium sulphate would remove tarnish from silver without rubbing. Unfortunately, he is dead now. There used to be a product on the market called Tarnex but I have been unable to locate the product.

I will be very cautious in my attempts to restore the image. I would suggest anyone reading this who has never seen a daguerreotype should search the name on the internet these photos are something to behold.

Ronald Mesnard
- Derwood, Maryland, USA

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What is normally used is a mild thiourea ⇦ this on eBay or Amazon [affil links] solution acidified with phosphoric acid to a very low pH. The solution will damage the image to a lesser extent than the other cleaning solutions such as Cyanides, and other thiosulphates. Sputtering in H2 is less damaging but who has the equipment?

Ron Mesnard
- Deerwood, Maryland, USA