August 10, 2014, What happened to the color of my stamp?
The collectors sometimes first think that their stamp album pages have plasticized PVC in them and that has caused the discoloration. The philatelic industry has almost universally mistakenly referred to this process as "oxidation" for many years. Thankfully in the case of SAFE Stamp Albums, we know that there is no plasticized PVC in any of the pages.
If your stamp is in archival stamp album pages, then the actual cause is environmental contaminants in the air, in which the correct term is actually "Sulphurization." Below, I have paraphrased some comments from a recent editorial in the American Phlatelist.
Sulphurization is an unintended and undesirable chemical process that alters the natural color of stamps printed with ink containing lead. Philatelists often assume that prolonged exposure to oxygen is the cause of this browning. It is actually the traces of sulfur in the air that combined with the metallic component of pigments to alter the surface of the ink coating and our perception of its color. A sulphurized stamp represents that progressive damage over a period of time.
Many also ask whether this sulphurization can be reversed? And the answer is yes, by oxidizing the stamp. For used stamps, a gentle bath in an over-the-counter hydrogen peroxide (a 3% solution), followed by a rinse in a clear water will usually restore the color in less than a minute. Peroxide in its pure form is a very strong oxidizer. Obviously mint cannot be immersed in hydrogen peroxide without destroying the gum, but with practice, they can be fumed. However, NEVER ATTEMPT this yourself without first practicing on some common examples.
Some philatelists argue strongly against the use of peroxide on sulphurized stamps, calling it a form of alteration such as re-gumming. However, I personally think it is more like restoration or conservation in bringing the stamp back to its former beauty. Either way the choice is yours. But remember to keep your stamps as safe as possible in SAFE stamp albums!