Self-contained covert image

摘要: A hidden image, which can be made detectable by rubbing, is produced applying to a substrate surface first ink-like material in image configuration, then second cover the and an area surrounding image. Each of materials contain one color-forming pair reactants are colorless or light colored their unreacted states, but together produce product when brought into reactive contact. Separation two assured encapsulating at least reactant pair. Reactive contact caused rubbing printed otherwise sufficient pressure rupture capsules, releasing intimate with other reactant.