Silver Coin Toning In Some Proof Sets

None of the mint packaging is truly air tight. Modern lenses and capsules are a very tight fit but are not really sealed at all, no welds, no glue. Some of the late 1970s and early 1980s packages were glued but not very tightly closed otherwise. The plastic sheeting used from 1955 through 1964 was sealed but many of those seals were compromised over time and the sheeting itself was not truly impermeable. Prior to 1955, no seals of any kind were used. Even in cases where mint packaging happened to be air tight throughout it's lifetime, the possibility of contaminants inside the packaging (on the coins originally or in the other materials) exists. It is also important to remember that simple toning has no affect on coin value. It does affect some collectors enjoyment of the coins, sometimes in a positive way, sometimes negatively. Also, there is a difference between toning (a reaction involving the metal alloy of the coin itself) and residue (any material deposited on the surface of the coin, not involving the molecular structure of the coin's alloy). Residue can usually be safely removed and probably should be as long as it is done properly. Toning is another question since removing it does alter the original surface of the coin and therefore is a form of cleaning (usually considered acceptable). Some residues will also cause toning and it is often not possible to remove the residue without removing at least some of the toning as well. Care must be exercised to avoid creating a coin that is less attractive than it was to begin with. If one desires to collect coins that begin untoned and stay that way essentially forever, removing them from their original packaging and storing them in some sort of anti toning environment might be the only viable solution. In all but a few cases (some of those late 1970s and early 1980s packs) this can be easily done without any damage to the original packaging, which can be kept if desired to restore the sets to as delivered from the mint condition if and when wanted.

This brings up the question then, are 2x2s airtight? If not, what if they are taped around the edges?

How about this one.

Thank you for the comments. This would imply that environment triggers toning in these set coins. Would that specifically mean heat and humidity? That a proof set that to date has no toning is best kept in that condition by keeping it cool and dry?

I agree that, in general, SAEs don't tone well. It seems that different coins have different toning tendencies. Morgan dollars often have very attractive toning, as do Walker half dollars. Franklin and Kennedy half dollars seem to rarely produce good looking toning and often tone in ways that detract from the appeal of the coin. The fact that some people will pay ten times the underlying value of a coin for "monster" toning is beyond my ability to rationalize. I have seen coins that I would gladly pay an extra twenty or even thirty percent for just because of the way they toned, but the underlying coin has to come first and be the dominant consideration. Some proof Morgans are this kind of coin (and some are dark and ugly). Cameo proof coins seem to tone in a completely different way than satin proof or business strike coins. For most coins, getting them out of mint packaging and into well sealed containers and storing them away from moisture, light, and heat will keep them pristine indefinitely. For a few however, the source of the toning is something left on the coin by the mint, and they are going to tone no matter what. An untoned coin will always retain its initial appeal. A toned coin may or may not, and it seems that more often the toning is a detractor.

No, but the Mylar lining is.

I still agree with you, though. The seam will always be the weak point. It is difficult to guarantee that the tape and Mylar will always make a good seal without any exposed cardboard between them.

A self-adhesive 2x2 may be air tight, but I would not want to make that claim.