Abstract: A method and an apparatus for applying chemical watermarks to a substrate, e.g., paper, using a digital printer which prints ink in a dot matrix pattern. The ink may contain either a translucentizing agent or an opacifying agent. The printer is digitally controlled to print ink in accordance with a computer program corresponding to a desired pattern or image.

Abstract: A recording sheet for ink jet printing comprising a support having coated onto said support one or more layers receptive for aqueous inks, said coating comprising at least one film forming, hydrophilic polymer or a mixture of film forming hydrophilic polymers and imbedded in this film at least one trivalent salt of a metal of the Group IIIb series of the periodic table of elements or complexes which comprise trivalent ions of the metals of Group IIIb of the periodic table of the elements. In another embodiment the salts or complexes of Group IIIb elements are coated directly on the substrate surface without the presence of the film forming polymer.