Some time ago I took on the challenge of attempting a type set of German coins beginning with Wilhelm I all the way through the Euro. Turned out to be a very curious endeavor considering the history, political evolutions in the region, and military occupations throughout time. Not to mention the generally beautiful and artistic designs of German currency. The set is not yet complete, but I have made tremndous progress so far. One of the most difficult additions turned out to be the WWI military issues which were created for use in the occupied territories of Russia, Poland, and the Baltic States. This set consists of three denominations which include 1, 2, and 3 Kopeks. The coins are struck from iron which is very susceptible to rust and, in my experience, are practically non existent in higher grades. I was lucky enough to obtain a very nice example at the New York International Numismatic Convention back in January. The 2 Kopek piece (KM22) had great eye appeal and very minor traces of rust. Like most of my other coins I photographed it, sealed it in a 2x2, and placed it in its proper order in the album. Last week I looked at the coin again and saw that the rust had spread extensively. After some pondering I came to the conclusion that the coin may have been cleaned or treated prior to my purchasing it and has since reverted to its original state. That however is just a theory. I don’t believe that this is a result of improper storage simply because I’ve kept coins in this manner for many years. Additionally there is another iron coin on the same album page which has been there longer and maintained an unchanged appearance. The attached photos are the before and after of the same coin. Would be interesting to hear some ideas on how or why this change occurred. I must add that this coin continues to be one of my favorites in the set and I have no regrets of having purchased it. It’s still a beautiful piece and the history is incredible. Also a pretty cool story to go along with it. Can’t wait to find the two missing denominations. VZ
It may have been treated before hand which, depending on how it was done may have made the surfaces more susceptible to rust formation. Having said that, rust isn't going to just appear without the right conditions, which means improper handling (possibly before you acquired it) and/or improper storage. Did you treat the coin before putting it in the flip and after you handled it for photographing? I have a similar Hungarian set with MS63-65 iron, steel, and zinc (much more problematic than iron) coins from both WWI and WWII. For these coins I treat them with acetone (I treat all coins with acetone before they are stored because I don't know how they have been handled before entering my care), VerdiCare (for zinc), and then I apply a tiny amount of light mineral oil to protect the surfaces. The only way the WWI era coins really survived without corrosion in high grades was from being kept oiled.
I agree with the possibility of it having been treated before I acquired it. I try to avoid treating or cleaning coins in any way so it was stored in a 2x2 just as I got it.
Ok, but how do you know how it was handled before you got it? That's the danger. Acetone removes oils from handling and other organic contaminants (PVC residue, adhesives, etc.) from the coin without adversely affecting it. You don't want to store a coin long term with these contaminants present. Acetone also assures the coin is completely dry before storage. Proper cleaning (a.k.a. conservation) and proper protection of the surfaces is a must for WWI era iron. By the way, I would also suggest keeping a coin like that in an archival all-mylar flip like a saflip. Cardboard wicks moisture out of the air and is not ideal storage for this type of coin.
Don't run me out of town on rails for suggesting this. Used to be a previous generations numismatists would conserve coins with a light coat of shellac. I cannot fathom any scenario where raw iron will not rust unless the surface is protected somehow. And shellac is relatively simple to remove from the surface when you don't want it there any longer. Just throwing it out there for consumption.
Downside with shellac is that is will discolor over time and any moisture or other reactive stuff can continue to cause corrosion under the coating. (Not a slam Randy, just an FYI) There is a product called RenWax that is used to preserve the finish on ancients (there was a recent thread on the Ancient Forum here). Maybe that microcrystalline wax would work?
A thin coat of light tool oil does the job as well. As I mentioned above, that's what I use for these types of coins. This is the product I use: https://www.amazon.com/Starrett-1620-Tool-Instrument-fl-oz/dp/B000KUA2FI/ After the acetone application, I put a couple drops on a q-tip (the kind with the solid tips work best) and then I gently roll it over each surface of the coin without applying any pressure. Think along the same action as a wheel rolling over a surface. There is no rubbing.
Everyone always talks about copper coins turning, but I think iron is even worse. The problem is, the natural oxidation and patina formation that we love on silver coins is also occurring on the iron coin. Only, with iron coins, that patina is rust.
I agree. Iron is really tough to find in a high grade. I’ve yet to encounter one of these problem free and in mint state.
What’s nice about copper and silver is that when they corrode, they form a passive film and further corrosion is significantly reduced. Iron corrosion is not self-limiting and does not form a passive film. I believe the difference is due to iron oxides being of great enough volume that it doesn’t strongly adhere to the uncorroded metal and the corrosion product flakes off. For silver and copper the atoms in the film are more compactly arranged and can more strongly adhere to the metal.
