This 1988 airmail stamp honoring aviation pioneer Igor Sikorsky is one of a handful of U.S. stamps produced with gravure and engraving—a technically difficult combination. Most of the stamp was printed in gravure, but the crisp VS-300 helicopter was produced with engraving.
Like many modern U.S. stamps, this one includes a “taggant” visible only in ultraviolet light. Taggants allow sorting equipment to locate stamps on envelopes. They can be embedded in the paper or added as a coating; here, a tagging ink was mixed into the special light blue ink.
Artwork, Model, and Die Proof for 36¢ 1988 Sikorsky Airmail Stamp