Encoded security document.

摘要

Documents (1) are encoded with at least one thin, transparent coating (3, 4, 5) normally invisible, but detectable by electrical capacitance measurement. Each document consists of a substrate (2) on which is applied (A) at least one of the thin coatings, and (B) conventional printing, preferably intaglio (6). The coating includes particles (8) sputter deposited into the substrate surface and is applied before or after printing. The coating is confined to a limited area of the substrate surface and itself constitutes a code for identification. A second coating can be applied so that all areas of the surface have the same appearance to mask visual discovery of the first coating.