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.
Alkalis are often present in phosphor inks to prevent polymerization prior to the printing.
After printing, the alkali is absorbed by the paper. The alkali should not harm the paper, and it may add to its life by neutralizing acidity. Some collectors see the various bars and coatings in their many sizes and luminous characteristics as varieties. These characteristics do change over time. It is virtually impossible to retain the tagging characteristics in their original condition.