"Moth and rust doth corrupt." Like all hobbies, stamp collecting has its drawbacks. Its major drawback is that the stamps themselves are impermanent pieces of paper coated with gum Arabic, and are in a state of slow decay. The gum attracts moisture and this then promotes fungal growth. As the years pass, "rust doth corrupt". The brown stains that slowly appear on the stamps is actually called "rust". Inevitably the stamps just rot away. The older they are the more prone they are to rust. And of course, the older they are the more expensive they become. In the early days the stamps were stuck into paper albums with a moistened hinge. The whole process was virtually designed to encourage the growth of fungus, and grow it did. So, with old stamps the advertisements usually run "In fine condition but with a few rust spots." The rusted-away examples don't even get advertised.
How to protect your stamps, that's the question. I was giving a lecture at a stamp club on one occasion and asked for ideas on protecting stamps from rust. A lady piped up, "just coat them with talcum powder." Horror of horrors! Most powders contain perfume and perfume is made from essential oils. She now has a collection of oily stamps and so has devalued them by 80%. Unperfumed talcum powder is OK, but commercial powders are a "no-no." Putting the stamps in a sealed cupboard with a moisture absorbent is about the only protective aid. One dealer even suggested that with valuable stamps we should give up trying to keep them with their gum. Best to wash the gum off and save them, rather than keep the gum on and see them slowly "rust" away. The only trouble is stamps with undisturbed gum are worth more than with disturbed gum and very much more than those without gum.
In my collecting area, Angola, many stamps spent half their life in a humid tropical area. Rust just loves heat and moisture. Not only that, but when the stamps were shipped to Angola from Portugal, they had to interleave them with waxed paper to stop them sticking together. It was so damp the stamps ended up sticking to the interleaved paper, so "disturbed" gum and rust is par for the course when it comes to Angolan stamps. So, "rust doth corrupt", and not just stamps.
As I sit watching my little pieces of paper slowly rotting away, with the hope that thieves do not break in and steal, I am reminded of the words of one of my mates who summed it up this way. "It's all going to burn!" Well! who can argue?