I soaked a bunch of stamps in water for a couple hours this morning and noticed that some of them had radically faded! I could get the back paper off of them, but the stamp was faded to much to be worth anything in my collection.
I'm not sure if soaking is worth it to me if that is going to happen. I think in the future I'll just cut around them. Sure it'll ultimately make the pages thicker in the album, but I'll just get a bigger binder!
Stamps printed in aniline inks are water soluble. Of particular note are early stamps from Great Britain an colonies (particularly green and shades of red: carmine, red, scarlet), and the Netherlands and Netherlands colonies, namely the larger, square Queen definitives.
There are some more, but that is about the most of it. As someone stated, pay attention to the catalog warnings.
