I am going through some rolls I have had for over 20 years stored in my house in wooden boxes. The coins themself are either in coin wrappers or coin tubes. I thought I would look for some errors but noticed some coins, that were BU, have now black spots all over them. I thought humidity and climate would cause this but can not understand how this could happen the way they were stored. Yes the majority of the ones I noticed came from coin wrappers not coin tubes but there are some in coin tubes also. I guess now they are pretty much just worth a cent now. Of course all coins not BU are not effected. In the future I guess I will put all BU rolls in coin tubes taped really good, unless someone suggest something better.
Copper is a VERY reactive metal. Oxygen causes it to "tone" quickly as well as many other chemicals. Sulphur, for instance, is found in many papers (like coin paper wrappers) and it too can cause unattractive spotting/toning on copper coins. More on sulphur spots... Carbon spots (what some collectoris call them) aren't actually carbon, When copper reacts with sulfur in some form or other, it becomes copper sulfide and the process does indeed involve oxidation. Hence the color change. Many coin graders and conservators agree that "carbon spots" are usually the result of droplets of saliva (and an occasional dandruff flake) that have landed on coins while they were being handled and talked over. Take a proof coin and cough on it...watch it develop spots later. Don't DO THAT, bit I am making a point that you should NEVER exhale over nice proof or BU copper coins. As such, it is not that we eat raw sulfur, but some foods do contain more sulfur than others.
Forgot to add: Copper and silver will tarnish in reaction with hydrogen sulphide, a pollutant given off by decaying animal matter (which is naturally present in the atmosphere). However, some paints, textiles and other household materials also emit some sulphur-containing organic compounds and these also cause copper and silver to tarnish. That is why copper and silver are not NOBLE metals like Au, Pt, and Pd which are metals that do not tarnish or oxidize.
Thanks for the education on the many things that can cause spots. Now my next question would be does anyone go through the effort and coat their coins with a light film before storing? What other things can be done to help preserve the tone? thanks in advance Randy
