Tarnish Protection for $0.01

MrSpud

After reading the book Coin Chemistry by Weimar W. White, I wanted to pass along a tip that I thought was a good idea. The author had done a lot of experiments using copper impregnated bags to store coins in holders in to prevent tarnishing. The copper is supposed to be more reactive with tarnishing gasses than the coins, especially if they are in holders. The author did experiments with coins in various slabs and holders including Kointains and found that all of them slowed down tarnishing to some extent but that none of them prevented it (Kointains did the best though, slabs didn't do as good as the Kointains) except if in the copper impregnated bags. The author said that if the bag starts to turn brown it means it has absorbed a lot of tarnishing agents and should be replaced.

Only footnotes in the book said the copper impregnated bags weren't commercially available anymore and said to use intercept shield products instead. The author of the book also mentioned that a good way to protect coins is to put a uncirculated copper cent or two into a ziploc bag along with a slab or a coin in a holder. The copper cent, like the copper impregnated bag, is supposed to be more reactive than a coin in a holder. If the cents start to turn brown it is supposed to be time to change them.

The author also theorized that most old proofs became tarnished and lost their mirror finishes because they were stored in wood or other containers that either didn't protect the coins from atmospheric gasses or, worse even, caused the coins in them to tarnish excessively. The author also said that some coins escapsed this fate, supposedly from being stored in tins or ceramic containers that were more protective.

I did a patent search on the copper impregnated bags and also on intercept shield products. It appears that the intercept shield products also work because they have copper particles dispersed into polymers in them. Only they seem to be doing some tricks to increase the surface area of the copper so that it absorbs tarnishing agents better. Here are links to the patents for those interested in seeing them.
Copper Impregnated Bag Patent

Intercept Patent

After reading these, I really like the idea of using uncirculated copper cents as a cheap substitute for commercial tarnish preventing products. I also think the copper cents would be a good early warning system to let you know if where you are storing your coins is potentially harmful to them. If the cents begin to tarnish rapidly, store them somewhere else or put them in a protective container. Only, I think the cent idea could be done one better if copper foil is used instead of the cents. I picked up a roll of copper foil at a craft store and I plan on using a square of it instead of the cents or even lining the bottom of containers with it. This way, the copper can be used for protection and as an early warning system and I can "recharge" its reactivity by occasionally sanding it with emery cloth to remove any tarnish that builds up on it to keep the copper more reactive.

Regards,
MrSpud

sliderider

The only problem I can see with that is that cents these days aren't much more than zinc electroplated with copper to give it color. Probably not enough copper to stop the chemical reactions for very long. I don't know, do you think maybe storing your slabs in a copper box of some kind might work? Maybe if someone has an old copper pot or kettle they can do an experiment by placing a few slabbed and unslabbed coins in the pot and checking periodically to see if they tarnish or if the copper draws the chemicals in the air away from them.

MrSpud

Yeah, it would be important to use an older cent to make sure it had enough copper in it. An old proof cent might even be better because it should be easier to see the beginning stages of tarnish on it. Or, if you are like me and don't want to sacrifice actual cents, the copper foil with an occasional sanding to keep the copper really reactive. Just make sure you get real copper foil. The roll I picked up just says copper, but it might actually be some alloy. I think it is good copper though, because one package of it on the store shelf had a tear in its plastic package and the foil inside was very tarnished.

I like the idea of using a copper container for coin storage, that seems like it should work good. Especially if the inside is cleaned about once a year or so to remove any surface tarnish to keep the copper reactive.

Neptune

thanks for the interesting data - I was just looking at that book yesterday - do you recommend? Any other interesting parts?

magikbilly

Hi MrSpud,
excellent post! A great article with much useful information.

Thanks!
Billy

ScarsdaleCoin

this would be very similiar to what boaters do to outboard motors putting zinc on the prop....

MrSpud

I enjoyed reading the Coin Chemistry book, I thought it was pretty good. It is a thin book, basically a compilation of the authors experiments on coins. We cleaned up the house the other day and now I can't find the book, but I'll give some highlights from memory. The author did a lot of experiments exposing coins to controlled amounts of hydrogen sulfide gas and tested the various slabs and holders to see which offered the most and least protection. The author doesn't hold toned coins in too high of a regard and seems to prefer well preserved coins with less tarnish or toning on them, but even those who like toning would get some insight into the factors involved from his discussions. He also discussed theories on why some old proof coins still have mirror finishes where most of them have lost their finishes. He also discussed what happens to the surface of coins if cleaned in various ways also. There is more stuff too, but I cant remember the details.

Maybe when I find the book I'll post another tidbit or two. I'll end the post with one more thing I remember. In one part of the book, the author made a funny recommmendation to test slabs by putting the seams to your lips and to either suck or blow air to see how well sealed they are. Well, just today I read a letter to the editor in Coin World that criticized this advice. The person who wrote the letter said that sucking on the slab should be OK but not blowing into it. He was concerned that people would blow moisture into the slabs and ruin the coins and he wanted to warn people not to try this. I can think of several humorous things to say about this but it would be too easy...