Stamps on paper

When I was a kid, my dad would bring home all the stamps accumulated in his office building to be soaked. After some minor tests in small containers, I decided to use the bathtub.  The first try in tepid water went well especially if you wanted 1,000 copies of the current regular issue of the U.S. 3 cent stamp.  [Later, I was able to trade bulk quantities of common stamps with others for individual items I sought.]  The second time, the water turned red, and I learned to check the colors of the paper backing the stamps to avoid soaking envelope paper that may have water soluble colors.  The third time I found out that many foreign stamps had water soluble inks that caused the colors to run giving the stamps an off-color, faded appearance. 

At that point, I learned not only to check the paper to which each stamp was affixed but each stamp itself to see whether any of its inks were potentially water soluble.  Water solubility was a common security device used by a variety of issuing governments to prevent an uncancelled stamp from being soaked off its paper and being reused.  That transition most often occurred when the printing of a country's stamp issues changed from engraving to lithography or typography.  Few catalogues provide information on whether the ink will run or not.  Most important is to test a similar stamp (you are willing to destroy) from the same country issued in the relevant time frame to see if the special stamp you want to soak may have water soluble ink.  If so, do not soak the stamp you want to keep, or be willing for it to fade. 

There is nothing wrong with soaking in water, if you are careful.  There are a variety of solvents for sale other than water which may be able to loosen or dissolve the glue on a stamp can be separated from the paper backing. 

If you soak stamps in water, you can place the soaked stamp on newspaper (that is printed with black ink only which you can test in advance to make sure it will not run) to dry.  It is recommended that any excess water be removed when you first place them to dry.  Do not put stamps on top of each other or you may have to re-soak because all of the gum did not come off in the wash.  That excess glue also is of concern if you try to press them during the first dry as they may stuck to whatever you use to press them.

Sometimes, for a stamp you care about, you can use a moistened "Q-Tip" and, with time, work the envelope paper off its back. 

Problems do arise when a stamp was issued without gum (like many of the early issues of the PRC) as anything could have been used to affix it to the mailing piece.  Putting two such identical to soak can cause the glue used for one damaging the other stamp.

Yes, there are ways to get a stamp off paper leaving much of the gum intact and ways to add gum and "smooth" it out so that the stamp looks original.  My concern is that it is an unfortunate practice today of some to take hinged or badly hinged mint stamps and make them look like "mint, never hinged" stamps.  The problem is that this destroys trust in the hobby as such stamps can and are being offered for something they are not and at false prices.  I knew a dealer who contracted with a local utility company to buy all of the emptied envelopes that had been used by its customers' to mail in their monthly payments.  I was a great idea and I obtained many unusual stamps of the time from him.  I day when I went to see what new items he had obtained, he told me he would no longer have any.  When I asked why, he said he had been indicted for selling the uncancelled stamps he got as ungumed mint stamps that could be used for mailing.