Fingerprints are one of the most important things that link a suspect with a crime scene. Even though that fingerprints are not always left by a criminal, the crime scene should still be examined for them. All people have distinct friction ridges on the skin of the fingers. In leaving an impression, an outline of the ridges is transferred and duplicated by oil, sweat and other substances on the object handled. The impression is usually not visible. Fingerprints not visible are called latent prints; so something must be done to make them visible.
The most common way to make them visible is to “dust” an object with fingerprint powder. The color of the powder should contrast with the surface, such as black powder on light-colored backgrounds and white powder on dark. An alternative to using powders, is using chemicals. The most common to use are Iodine, ninhydrin, silver nitrate, or cyanoacrylate esters. The process involves fuming, spraying, brushing, or dipping the object in a solution of the chemical. Yet another way to make fingerprints visible is to use radiation. There are two kinds of radiation to use, Ultraviolet rays, and laser radiation.
A latent print requires a suitable surface for it to be picked up. Porous surfaces such as unpainted wood and some kinds of paper are unlikely to yield a useful impression. Smooth surfaces like glass, enamel, and glossy paper are ideal to lift the print if you are lucky enough to get it.