I'm kind of baffled.. So, a little history here. Whenever I buy a silver coin, I clean it, then put it in a tube or airtite. (I know, controversial) And I realize that with exposure to oxygen they will all eventually re-tarnish. But here's the real mystery. I opened some old tubes today of some old half-dollars and I noticed the same thing in each tube. These have been in that tube for over a year without inspection. About one out of 5 had re-tarnished, slightly. These were all cleaned at exactly the same time, and have spent the same amount of time in the tube. I also noticed a tube of silver eagles, which I did not clean (because they were all brand new when I got them) have done the same thing. So why do some coins re-tarnish faster than others when they are all in the same environment, for the same amount of time?
I hope you are not cleaning your coins abrasively. For circulated coins dip is also a bad idea. Better to just use acetone. Circulated coins are more resistant to retoning. Perhaps that accounts for the difference?
Try NEVER to clean any coin unless you dug it from the ground or it had fire damage and need to do this to identify it. Air Tites are a good idea though.
Any valuable coins should be left w/out cleaning (an acetone dipping's ok) barring evidence of pvc deposits. You may find to your dismay the surface is damaged in a way that won't let you sell it to recoup your funds and move on to a better piece,I did! Tough for me! ha ha
Surface science is very complex and I don't understand that much about it. VERY small amounts of impurities on the surface can radically affect the way the metal reacts with substances in the environment. I kind of want to say the reason a coin tarnishes (or tones if you like it) is the same reason a dog barks...because it wants to.
Ph levels may have something to do with it. I had a unc. silver dollar in type set holder; the face was behind a thin sheet of clear plastic, the reverse was against a piece of cardboard. I discovered after more than a decade in this holder the face was unaffected but the reverse had developed a beautiful patina -- probably from contact with the acidic cardboard in an airless environment.
Slight differences in pH, surface impurities, and moisture levels will all affect toning. My guess is that whatever you cleaned the coins with may have remained on some of the coins, causing different toning.
What the OP is describing is something that is so common that it often escapes notice, that being that some coins tone, sometimes rapidly, and others simply don't - even when they are kept in the same environment. Now you could say that the differences were due to certain contaminants being on one coin and not on another because the coins came from different sources. And that sounds like a reasonable explanation. But how do you explain it when all of the coins came from the same original source, were all stored in the same way and in the same place, and yet some toned and some didn't ? Things become a bit more complicated then for then there are no "reasonable explanations". Or at least no readily apparent ones. For example, let's say a collector buys a small bag of coins or roll of coins directly from the mint. And then stores them all in the same and same place, be it in an album, individual coin holders, or 2x2s, or whatever. And yet some of these coins tone, fairly rapidly, and yet others do not. And yes, this is an extremely common occurrence, and has been for over a century. And yet people still try to say - well this coin had this on it or that on it and that's why. And I understand why, it's because they can't think of any other reasonable explanation so they feel that must be it. Do I have an explanation ? No, not really, but there are several possibilities that come to mind. Perhaps it is due to the coin storage medium itself, the album, the individual 2x2s, or other coin holders like individual envelopes - perhaps some simply have more sulfur in them than others, perhaps some merely drew more humidity out of the air than others. I doubt any of could ever really know. BUt what we do know, and know for a fact, is that some coins do tone more rapidly than others. And even though can be because a given coin came from a different source, that is not always the case.
Now that you mention it, I noticed our Thanksgiving silverware didn't tarnish at the same rate, either. BTW, just a tip. Polish your silverware, not your coins.
In your case - there are a thousand individual differences capable of causing differing toning rates - your cleaning process differing just slightly between each coin is likely the major factor. It's irrelevant in this case because cleaning the coins ruined them (it's not "controversial," it's vandalism), but it bears mentioning that an atmosphere capable of toning coins in the middle of a tube is pretty destructive.
Well, there isn't exactly lots of air circulating inside a tube. So, the coins therein either had to get a large-enough dose of the sulfur required for toning from their brief atmospheric exposure between cleaning and storage, or the atmosphere in which they were stored had to have enough sulfur in the atmosphere to penetrate a sealed container and reach between stacked coins. Even if it took a full year, that's disconcerting.
