See also the instructional video "Evidence Photography — Alternate Light Sources"
Some materials will absorb ultraviolet, while others will reflect these radiations. Some have partial reflection. These effects can be recorded photographically suing ultraviolet radiation. Black-and-white films are sensitive to most wavelengths of ultraviolet. By using a filter that absorbs all visible light but passes ultraviolet, it is possible to make a photographic exposure with just ultraviolet.