I had to jump in on this because I had what I thought to be a fluke happen a second time. Sorry for being somewhat off topic, but at least in an appropriate threat...
I've been using the copper strapping you would use to hang plumbing in your basement (happens to be what was on hand). After an embarrassing first attempt I figured out pretty quickly to burn off the lacquer coating from them before cementation.
Anyway, the last 2 cementation attempts I did were from rather concentrated solutions, roughly 80% of saturation. I took some advice from amesametrita and held the pH right around 3 or so with a few drops of nitric a couple times and got absolutely beautiful silver crystals that were dense, well formed, non-adherent, rinsed very easily, and melted like butter.
However, about half way through (half the expected silver dropped) the copper strapping got silver plated. It was a very nice looking very shiny, almost polished looking solver plate on copper. Of course it stopped cementing any additional Silver.
Obviously I can hit it with nitric and get my little bit of silver back. Also, I was in a hurry and hit the rest of the solution with HCl (in retrospect I should have heeded the warning of many on here and avoid Silver Chloride at any cost).
Can anyone tell me what happened in this solution? The feed stock was a bit of dirty cemented silver (too much copper) and some silver nitrate crystals so I can't imagine there was much in the way of foreign contaminants. The only thing I can think of was too high a concentration in solution. The only other possibility I can come up with is that it is quite cold where I have it set up, but it can't be below 45-50 F.
Thoughts?
