Ive noticed the MS quarters in my dansco album are starting to get a goldish toning after being in the album since 99 but what makes a coin (especially those beautiful peace dollars) acquire a rainbow toning?
This thread explains it better than I can: http://www.cointalk.com/t84670/ Part of it has to do with the surface of a coin. Microscopically, there are ridges in the coin's fields, and because the oxidization which causes toning in silver fills these creases, it reflects certain colors. The differences in depth in some of these ridges causes different colors to reflect, causing rainbow toning. Different coins have more or less even ridges, causing a uniformity in the toning color, so it is rarer to find rainbow tones on some coins than others.
