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.