Method of printing and adhesion that allows hidden characters to be revealed

摘要

The multi-layer document has a design or character printed on the first sheet (2) with an ink that has a known adherence. A second sheet (3) is glued over the top of the first sheet, using a glue that has an adherence greater than that of the ink on the first sheet. The design or characters may be formed in different ways. The first sheet may have variable opacity, allowing the design to show by transparence once the top sheet has been removed. In an alternative method the designs can be printed in reverse and become visible on the underside of the top sheet when it is removed.