EntityQ1136406· pop 23· linked from 217 articlesinvisible inkSign in to savesubstance used for writing which is invisible and can later be made visibleConnectionsheatEntityultraviolet radiationEntitypotassium ferricyanideEntityWorld War IIConceptbookEntityGeorge WashingtonPersonWorld War IConceptBill ClintonPersonOvidEntitymetalEntityCitrus × limonEntityglassEntityInternational Standard Book NumberEntityiodineEntitysoapEntityacidEntityplasticEntityArabsEntitysoybeanEntityCentral Intelligence AgencyEntityCategoriesEspionageSteganography