Fugitive ink

Fugitive ink is a feature where ink fades or runs with enough moisture. It can be a security feature of sorts to prevent re-use. Fugitive ink is a fact of life with the purples and greens of the Victorian and Edwardian stamps of Great Britain and its colonies. Until you have mint examples to compare, you will not be aware of the changes that soaking these stamps has caused. Similarly, any bright red and rose stamps from around the turn of the 19th/20th Century should be suspect. The Netherlands Indies definitive sets of the 1930s were deliberately made with fugitive ink.

 File:HK compare.jpg|Hong Kong. With the heavily faded head on the left example due to soaking, we learn that the stamp was printed in two similar colors of different composition. The right stamp is itself in two very slightly different colors, truer if not true to its original color. File:Neth Indie 5s compare.jpg|Netherland Indies. The left stamp has been soaked and this is the result. Note that the cancel protected the ink to some degree. 

Purple/violet/magenta cancel inks, often used by many Central American countries are fugitive, as were the similar inks used by US post office for parcels and registered mail. Stamps known to be on chalky paper can lose ink when soaked as can some more modern issues printed on very slick and shiny paper. The solution in handling those suspected to have fugitive inks is to either not remove the paper or hinges or to use the method of floating to remove backing paper.

See

 * Floating

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