These inks are more sensitive to solvents than other printing inks. They dry by absorption into the paper and by atmospheric drying. At various times, fugitive inks have been used in printing postage stamps, and these cause problems. Fugitive inks fade over time and run when the stamps are soaked off paper, even to the point where the colored ink will dye the stamp paper, including the back of the stamp. The addition of a teaspoon of salt to four cups of cold water used in soaking the stamps from the paper will stabilize the ink and reduce running to a minimum.
Some countries purposely use fugitive inks to prevent re-use of uncancelled washed stamps.
Sizing is discussed in another section on this website. Collectors who live in areas where tap water is chlorinated may have noticed that used stamps, when soaked off paper and left in the water for half an hour or more, will brighten up considerably. This is due to the miniscule amount of chlorine present in the water. Stamps should not be left in the water longer than is necessary to separate the stamps from the adhering paper because water softens and changes the paper fibre. This solution stabilizes most inks and brightens the stamps.