Foxing - What Should I Do?

All the foxing I have seen has come from paper stored in a damp environment. There certainly can be different types of foxing, but it's bad news when you see it. The worst foxing I have ever seen was in a book I bought from the APS book sale! It turned out being one of my worst philatelic purchases!

I have seen where foxing does not spread and I have seen where foxing spreads from the stamp to the page. It depends on the cause of the foxing. Some countries used cheap gum on the back and the stamps fox. Some stamps are found in moist climates and they tend to fox. And some stamps were kept in the basement or attic and foxed. There are many reasons why stamps fox.

You're claiming that there is no factual basis for the claim that mold is the cause of foxing, but the case has been made (https://pmc.ncbi.nlm.nih.gov/articles/PMC4959533/) that fungi and their chemical byproducts cause staining by breaking down organic materials in the paper and triggering oxidative reactions:




Not sure why you're waving away such research as "internet misinformation." If you've found a scientific paper that definitively proves that mold/fungi have zero to do with foxing, then please present it here for others to see.

Otherwise, it's reckless to dismiss the leading hypothesis of foxing formation (namely, that fungi and/or its byproducts cause the spots) as baseless nonsense. It's obviously a widespread problem with stamp collections, and many turn to this site as a source of information and counsel. Erroneously dismissing valid research isn't doing anyone any favors.

These spots are called "stockflecken" (foxing) in Germany.
Mint stamps affected by foxing are no longer desirable to collectors.

There is a chemical cleaning agent direct Link to seller page of LINDNER that works well and produces excellent results on ungummed or canceled stamps.

I am pretty shure that it is available in the usa as well, because the shipping costs are insane.

Unfortunately, stamps that have been chemically cleaned are also visually affected; the paper of such stamps becomes unnaturally white after treatment. Colors may lose intensity, and optical brighteners remain in the paper after cleaning if the stamp is not sufficiently soaked afterward.

To reduce or prevent the spread of foxing, I place my new purchases in my freezer for 2–3 hours. Caution — just because it's cold doesn't mean it's dry. Anyone who leaves the stamps in the freezer too long risks pressure marks, traces, or smudging on the gum.
The idea behind this is that the air moisture and paper moisture crystallize as the items cool. When the ice crystals form, they destroy the spores of the fungus that causes the foxing.

I've had good experiences with this method.

Two things can be true but don't let that stop you.

There is a chemical cleaning agent direct Link to seller page of LINDNER that works well and produces excellent results on ungummed or canceled stamps.
It's two solvents, actually.

The first one is potassium permanganate KMnO4
The second one is Sodium bisulfite NaHSO3
As with all chemical clubs, these are strong oxidisers that attack the paper structure (and you if you are careless enough) and kill living spores/fungi.
Before going fully chemical, you could try a hydrogen peroxide solution (which is used on "lead-poisened stamps") and check what happens.
All these chemical clubs (which includes household bleachers) should be attempted with used/ungummed stamps only.

For mint stamps, the problem is very difficult. What you can at least do is stop the spreading using either the above mentioned "deep freezer method" or use a strong short-wave uv lamp. My self-built 8watts sw lamp immediately starts to produce ozone (strongest oxidiser you can image) so if I placed a stamp (gum side up, obviously) right under the lamp, the combination of ozone/uv would kill any spores/fungi for certain. Doing that for too long and the paper will be negaively affected, obviously.

Removing foxing on mint stamps is something only experts can do (with some success).