I’ve seen numerous threads and messages regarding coins toning from sulphur (especially in paper), moisture, heat, etc. What about metal-on-metal? I would think that dissimilar metals being in contact would also lead to toning or some sort of corrosion. One of my eleven collections (or piles, in this case) consists of a small jewelry box shaped like a treasure chest. A year ago I filled the upper one inch of the chest with high-luster Sacs, cents, dimes, and quarters to give the appearance of a pirate’s chest filled with gold and silver. Last week I went through the contents to see if any any of the Sacs were of the Cheerios variety, and I noticed that the eye appeal of several of the coins wasn’t as good as I thought I required before being allowed to be a part of that “collection”. All of these coins are leftovers. Better ones of each year are in my other collections. If this set is doomed to toning, perhaps I would do better with it by applying a clear coat of fingernail polish to them ? I’ve read that collectors did that routinely a few decades ago to prevent (or at least retard) toning. Maybe a high-gloss coat (if there is such a thing) would give them an added sheen in addition to protecting them.
I don't suggest the finger nail polish trick. very bad. very, very bad. I will agree that dissimilar metals in contact will cause corrosion and pitting due to the potential difference created between the metals in the presence of water vapor. I don't think that the toning you described is from that. I think the jewlery box is not adequate protection from air and humidity. If you want to preserve the luster of coins such as these the best way is with airtites. I prefer direct fit but you can choose what ever type you want. In the least I would recomend 2x2 cardboard holders but they aren't nearly as good as airtites.
Air-Tites and flips kinda spoil the illusion of a pirate's treasure. What is the downside of using fingernail polish on coins that are not collectible ?
Damage to the coin aside, clear nail polish will just yellow and crack as time goes on. If you are determined to coat these coins, I'd invest in a higher grade (like $3 more a can) clear spray enamel from the hardware store. I have done well with Rustoleum brand on polished steel hinges in a showeroom to keep them from rusting. Just make sure to follow the can directions exactly. Most peoples first mistake with spray paint is holding the can too close to whatever they are painting.
I was considering that. However, in the few articles I’ve read where this used to be done, I never read anybody making that particular complaint. Nope, it was just an option. Maybe I’ll just fill it with Sacs only. Instead of a treasure of gold and silver, I’ll have just “gold”.
More than the contact with dissimilar metals ? I remember that wood can be a problem, and the chest is made of wood but has a felt lining in the little tray that sits on top that holds the coins.
It could even be the felt - or the glue holding the felt to the wood - or the wood. That's the thing about coins - almost all materials, except inert ones, put off vapors just from exposure to the air. These vapors cause reactions in metals. Ya never know what it's gonna be unless you know all of the chemicals in the various materials and how they react with each other and various metals. You are correct that dissimilar metals can react with each other. But typically other things affect metals much more rapidly, and often more severely, than other metals do.
Like the others posted it’s the box and the air that turned your pirate's treasure. ARRRrrrr!! …but not being one to pass up a chance to show my geekdom. Dissimilar metals corrosion is called “Galvanics”. Galvanic can happen when nearly any dissimilar metals make contact. It could be as little as steel panels on a ship in contact with the welds or rivets holding it together. However you need a good conductive liquid like salt water, acid rain, soda-pop and the like to start a reaction. If dissimilar metals are already electrically charged like the leads on a car battery, rainwater, or water vapor will still cause corrosion. GARrrrr!
Well, I only had maybe a dozen problem coins out of more than 200, but then the coins have only been in the chest for a year. I didn't study it, but my recollection is that at least one of the coins had some toning bounded by an arc that suggested it was in contact with another round object (coin). Of course, all the coins are thrown in together. However, when I put the coins back in the chest, I made an effort to insulate the Sacs from the clads with cents, on the pitiful theory that the cents are more similar in finish to the Sacs than the clads. The Sacs seem to be the ones that suffered the most.
Ahhh! Now we've stumbled on the problem. The reason most people do not like the golden dollar is it is really, REALLY susceptible to toning. The reason why is the oxide formed when the metal reacts with air is dark brown. This stands out significantly on a gold colored coin. With the silver and clad coins the oxide formed is closer to the original color so the initial toning is not as dramatic. People usually refer to this as loosing luster not toning even though they are one in the same. This is where a sealing coat or airtite is handy. The oxidation process can be accelerated by the presence of vapors in the air surrounding the coin. In your case the wood may be the source of the vapors but I would bet it is the glue used to attach the liner. Way to many thing can cause problems with vapors but one of the worst is a free chloride ion. This ion is why PVC is so damaging. A free Cl- ion is very reactive and just loves to react with metal. This reactivity is due to the location of the valence electrons and their affinity to develope full electron clouds. This is what actually allows the galvanization process. In short a salt ionizes into a positive and negative ion the negative ion forms a compound with the metal and oxidizes the metal. This oxidized metal may stay put and be considered corrosion or it may move. If it moves towards the other metal it can react with that metal as well. Now that the ion is already reacted it may decide that it likes the other metal better. When it drops the first metal ion for the second the first metal becomes deposited on the second. This process is very similar to electroplating and this is what I believe you were originally refering to with this post. As previously mentioned a transfere such as this is very slow and requires a soultion which has disolved salts, source of the ions, present in the solution. I had to geek out as well. Sorry for the length but I hope it helps. Anyway the answer to your toning problem is more than likely the Cl- ion in the glue, most glues have chlorides in them, reacting with the highly reactive alloy used in the the golden dollar.
Ummm, thanks, Morgan ! Interesting explanation. Much more informative than “very bad. very, very bad.” I used my magnifying loupe and, sure enough, I saw some ions jumping between coins. Does glue give off vapors forever, or just within some amount of time following application ? One thing I learned after reading through a book on woodworking is that woodworkers (not carpenters) much prefer to use joinery and glue in lieu of nails and screws wherever possible to join wood pieces. And, that is in the majority of their work. Even a three-foot wide dinner table might consist of three one-foot wide planks glued together. It’s surprising how strong the glue connections are, in some cases stronger than the wood.
GoldCoinLover, I’ve already got some black plastic storage boxes designed for Air-Tites that I use with some of my other collections. In this case, all I’ve done is dump in some high-luster coins into a small jewelry box (shaped like a treasure chest), just to give the appearance of a pirate’s treasure. There would be no point in preserving these coins that way.
