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Message:: [QUOTE="desertgem, post: 2125828, member: 15199"]Kurt, I recall Kodak stain remover from my work in non-digital photography- electron microscopy in the 60s, and it was the formula below ( I still have my college lab records <img src="styles/default/xenforo/clear.png" class="mceSmilieSprite mceSmilie1" alt=":)" unselectable="on" unselectable="on" /> ). If you modified it, I would be interested in how. If you look it up, the main reactant is the thiourea, which is the same active ingredient in the old Tarnx, and it would remove silver from the coin. Small amounts, granted, but still would microscopically release it. You can find articles on the net using it to remove silver from ore, so the surface would not remain as before. I am sure some luster would be lost. Noticeable or not would depend on the length of exposure. The main difference between this Kodak product and EZ-Est is that the citric acid is a weaker acid, and would be slower. That is why I suggest using the EZ-Est at a 1:10 dilution.  Silver estimating test papers we used to use indicates from a 0.0g/l and goes insteps next to 0.5 grams/liter ...up to 10grams silver/l. Much too large amount  to indicate any lost by either dipping solution, IMO.  Jim Kodak stain remover S-10:>Water.............................96oz>Kodak Thiourea.............10oz>Kodak Citric Acid...........10oz>Water to make................ 1 gallon[/QUOTE]