Series of inks, visually black in color, intended for the production of different shades of gray, which, once moistened with a little water or more simply with a wet finger, become colored (several shades available).
A print will thus change from black to color by simply humidifying it. A document secured in this way will be easily and quickly distinguished from an imitated document which will not have this reaction.
Printing of this type of ink is only possible using Typography or Dry Offset (the ink is sensitive to water). The color reaction will only take place once and is therefore irreversible.
