Fingerprints are an important part of a criminal investigation. Every person has a unique fingerprint, and there are different ways of collecting them from certain types of surfaces.
Almost any surface can hold a fingerprint when it is touched. People who study fingerprints are called fingerprint analyzers and they classify fingerprints into three categories: three-dimensional plastic, patent, and latent. Three-dimensional plastic prints are found “on soft surfaces [such as] soap, wax, wet paint, fresh caulk, etc” (“A Simplified Guide”). Patent prints are visible and latent prints are invisible.
Since patent prints are visible, most of them can simply be photographed. If better visibility is needed, powder and dyes can be applied to improve the quality of the print.
For latent prints, fingerprint powder can be applied and the powder will stick to the print. It can then be photographed. The print is sometimes lifted from the surface with clear tape and applied to a piece of paper to preserve it. The cyanoacrylate method can be used on latent prints as well. The object the fingerprint is on will be placed in a chamber and vapors from superglue are put in the chamber. These vapors will adhere to the print and it is then visible. Chemicals can be used as well as certain compounds attach to the residue of a latent fingerprint. A chemical called ninhydren will cause the print to turn purple, which makes it easier to photograph.
Fingerprints are left on surfaces almost any time it is touched. This makes collecting and analyzing these prints an important part of any investigation. If correctly identifying, a carelessly left print can lead investigators back to the perpetrator of the crime and help bring him or her to justice.
Source: Listed on Fingerprinting Part 2