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I am examining methods for storing silver bullion (both .999 fine and 90% silver) in such a way that it does not tarnish and want you to evaluate a suggested solution. I know there are commercial products intended to prevent or slow tarnish, such as cloth bags that are infused with silver particles. However, they aren't really suitable for bullion in my opinion. A proper solution should be

  • Very cheap
  • Work for a lot of silver, in varying sizes and shapes
  • Work for a long time

The suggestion in question is to store the silver in a somewhat air-tight container (like a ziploc bag or rigid plastic container) in which you also store some clean copper (perhaps bare electrical wire). In this situation, it has been suggested that atmospheric sulfur that gets in will react preferentially with the copper, leaving the silver pretty free of tarnish. From time to time the copper could be cleaned or replaced.

Unfortunately, the source who presented this solution did not seem very authoritative to me. Can you analyze the solution and give me your opinion? Please assume that tarnish is unacceptable, even though the silver is being kept as bullion and there are methods for removing tarnish.

Bonus question 1: Are there other atmospheric chemicals aside from sulfur that attack silver over time that one should worry about?

Bonus question 2: It as been suggested by some that the low density polyethylene in plastic bags will off-gas over time and cause additional tarnish or some other chemical reaction. I can't imagine this is sulfur but perhaps there is a chemical released that affects copper?

farnsy
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  • Give this a read when you can. Also, you might find this table useful in that regard O:) – paracetamol Jun 01 '18 at 05:06
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    Thanks! Am I to infer that in order for a copper object to best protect silver, it must be in physical (well, electrical) contact? I have only heard of this kind of thing in a liquid solution. Just looking to understand better. – farnsy Jun 01 '18 at 06:55
  • The classic way to protect silver is probably to coat it with cellulose nitrate varnish. – aventurin Jun 01 '18 at 08:16
  • @farnsy The way I see it, yeah. Galvanization works on the same principle. Even if we don't expect trash cans, lamp posts, nails, etc to spend time submerged in water, we still galvanize them. This is because corrosion is an electrochemical surface process; presence of moisture in air is conducive to this. Of course, if you can keep your container totally dry (which isn't practically feasible), then you needn't worry about corrosion O:) – paracetamol Jun 01 '18 at 08:56
  • It seems like aluminum (or zinc) is the usual choice for cathodic protection, not copper. But I'm not used to seeing aluminum get corroded by atmospheric sulfur. I'm sorry to be ignorant (high school chemistry only), but is the silver-sulfur reaction a good candidate for cathodic protection? If so, what's the right metal to use (should I be thinking of using aluminum foil instead of bits of copper)? – farnsy Jun 01 '18 at 14:57
  • Aluminium is good, Zinc would do it – Waylander Jun 01 '18 at 19:26

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