Philatelic Materials Subsidiary Page 17 Tagging Colors Varieties, and Tagging Changes Over Time Tagging Colors and Varieties Collectors who purchase tagged varieties, such as one tagging bar when there should be two, are advised to be very careful. Zinc silicate and sulfide pigments, commonly used in tagging, can be removed when the stamp has a portion of it boiled in water for two hours. The boiling water will also slightly change the color of the stamp's ink.
Most postal systems use activated zinc sulfide for tagging.
This fluoresces yellow green. Most Swiss stamps and some Belgian stamps use activated zinc sulfide with a small amount of copper. These stamps fluoresce a greenish yellow. A combination of tagging and bleaching agents will give a fluorescence of bright blue. Low concentrations of copper fluoresce pink, while calcium silicate activated by manganese will fluoresce pink to orange.