The adhesive substance on the back of stamps is called bum. The term derives from the words gum arabic which is a derivative of the acacia tree found in Africa. Before the introduction of self-adhesive stamps, additional forms of gum came into use in stamp production.
Dextrine also know as British gum is made from starch, achieved some popularity. A more modern gum was introduced in the late 1960s and was called polyvinyl alcohol aka PVA. There is another form of gum that is so invisible, it is virtually impossible to tell if it is still on the stamp or has been washed off.
Most modern stamps are now self-adhesive and have achieved a tremendous popularity with collectors. Self-adhesive stamp technology is still evolving. Self-adhesive stamps can be found from the traditional small definitive stamps to the colorful commemoratives and even coil stamps which are available in a roll versus a sheet format.
There are no firm rules on how to handle self-adhesive stamps. Some collectors believe self-adhesive stamps should be saved in mint condition, still attached to their original backing paper. Other collectors, remembering how badly the gum on older self-adhesives aged, recommend soaking the stamps to remove the gum.
On top of this is the fact that there are differences in gums on the self-adhesive stamps from various countries. The best advice is to play it safe and protect yourself by redundancy. This means that where possible save unused self-adhesive stamps that are both attached and unattached to the original backing.
If in the future the gum turns out to be destructive, the soaked examples you have will still be fresh. If the gum remains stable and the stamp value is keyed to the stamp having its original gum, you will have samples of these too.
Stamp gum poses quite a paradox to collectors. There is always the pressure to collect only ”mint, never hinged” stamps aka MNH, unless you prefer used stamps. MNH means that the reverse side of a stamp has positively no marks that disrupts the gum’s appearance such as from the use of a stamp hinge.
A stamp hinge is a specialized piece of paper, separate from the stamp itself and the album page that is used to attach a stamp to a stamp album page. Stamp hinges were commonly used in the past.
The problem with stamp hinges is that they leave a permanent mark on the gum side of the stamp. With the current hue for MNH stamps, hinged stamps have a lower value than stamps that have never been hinged.
Of course getting rid of the gum is possible, but that is not recommended. This is still one of the most hotly debated topics in stamp collecting. Generally stamp cum doesn’t age as well as the actual stamp paper itself. Climate has a major bearing on this too.
The value of older stamps is often based on the percentage of gum remaining. Removing the gum can lower the value of the stamp. Understanding how to care for your stamps is vital to maintaining the value of your collection.