I bought some bu silver rolls rolled in aluminum foil then put in a plastic tube. I left them in the foil (5 years?). Any ideas on this practice? Should I leave them in the foil?
That's an old timer's trick, brings back a lot of memories. A friend of mine who is no longer with us, known to some here & everywhere as Catman, performed an experiment with that lasted over 20 yrs. Only he did it with copper cents, not silver. End result - the coins stayed mint red and untoned. However, you will want to be careful. For aluminum, when it comes in contact with other metals and even the slightest amount of moisture, WILL cause a chemical reaction to take place that WILL harm the coins - especially copper coins. So if you are going to do it - keep 'em dry !
Actually the humidity has little to do with the reaction of dissimilar metals touching each other. The principle is really commonly used for the thing called a thermocoulple. It is the temperature change that causes the problem. Two dissimilar metals touching each other, bonded together would be better, will create an electrical current as the temperature changes. This current is the movement of electrons thoughout the metals that can be measured with a meter and is used throughout the world to measure changes in temperature. This same principle is why a ground rod can not be made of copper if the soil contains large amounts of aluminum. The coins in the Aluminum foil remained untouched possibly due to little temperature changes in the invironment that they were stored. ALL metals have the previously stated reaction when touching, however the more reactive a metall, the faster the reation. Such metals as Aluminum, Copper, Silver that are already high on the electrical activity charts would tend to react the fastest.
People used to use aluminum foil to prevent toning on the old double mint sets. I still run across them with shiny white coins wrapped in aluminum foil.
