A new method for searching latent fingerprints imprinted on plane surfaces using microscopic water particle and yellow light reflection was proposed. The microscopic water particle generated by a portable steamer was sprayed to the surface and the yellow light was irradiated obliquely from behind at the same time. The microscopic water particle remained as a hemisphere on the plane surface except for the latent fingerprint spots and the yellow light reflected by the water particle was observed through a yellow filter. The other color light mixed from sunshine or a room light did not interfere with the searching because they were cut off by the yellow filter before the observation. Thus latent fingerprints could be found as dark spots.
By using this method, latent fingerprints imprinted on plane surfaces made of plastics, metals, glasses and other painted materials could be found as dark spots even in a lighted room. The microscopic water particle on the surfaces disappeared spontaneously after the search and left no damage behind.
