STUDIES OF THE IRIDESCENT SHADES OF BUTTERFLY wings could lead to coatings to make tanks and planes invisible. As implausible as that sounds, British defense officials think research by physicists Peter Vukusic and J. Roy Sambles at the University of Exeter in Britain could have important military uses--and lucrative ones for industry as well.

Under an electron microscope, the wings of some colorful butterflies look like gray slate roofs. That's because the color we see stems from structure, not pigments. The wings are covered by tiny overlapping "tiles" 50 times thinner than a human hair. Each tile consists of multiple layers of cells separated by air gaps. Light penetrates this complex structure and bounces off the layers in ways that can give colors a haunting iridescent sheen.

By deciphering how variations in structure affect colors, the research could provide a recipe for microscopic plastic flakes to regulate color. One result might be the blackest black ever--a coating so black it would block even infrared heat rays. That could make a tank undetectable by night-vision systems. And extending the concept to radio wavelengths could make planes invisible to radar. Similar particles in inks could produce security seals that would make credit cards and banknotes harder to forge.

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