HOW TO... Spot a re-gummed stamp Mike Hall's detailed guide on how to beat the forgers and protect your collection
Stamps are famed for being “the most valuable asset by weight”. They are worth considerably more per gram than weapons-grade plutonium. Thankfully, they are less volatile! If stamps are the most valuable asset on earth, the gum on the back of the stamp could be considered the most valuable substance on earth. Collectors will pay massive premiums at auction for stamps where all of the original gum remains intact. For modern stamps, the gum is less relevant as it is relatively easy to buy them in Post Office fresh condition with clean full original gum. As such, modern mint stamps with full original gum are not particularly rare or valuable.
For stamps issued prior to 1900, however, very few examples have survived with completely undisturbed original gum. Most stamps would have been placed in stamp albums and, in the earlier days of our hobby, attached to an album page using an adhesive hinge. When this hinge was removed later it would leave a mark where some of the gum was lost. There are some rare stamp issues where there is no such thing as an example with full original gum.
In the UK, stamps with all their original gum are generally referred to as “unmounted mint” or abbreviated “U/M”. In the US, the terminology used is “mint never hinged” or “MNH”. With the original gum representing such a huge financial benefit, there's always a small number of unscrupulous people who will try to capitalise.