Types of fingerprints

In forensics, fingerprints are divided into three categories: direct, latent or plastic.

Direct prints are those that are intentionally laid down, typically using some type of ink that has been applied to the fingers or hands. Direct prints are used for record keeping purposes, such as for authentication on documents or for record keeping, such as when criminal's fingerprints are taken after they are arrested. Direct prints can be compared to latent or plastic prints to determine who deposited the plastic or latent prints in question.

Latent prints are prints that are laid down unintentionally, and are often difficult to detect with the naked eye. Prints such as these can be deposited any time someone's bare fingers come into contact with another object; the prints are often laid down due to the natural oils found on human skin, which are deposited following the pattern of friction ridges on the fingers. Since latent prints can be difficult to see and photograph, certain chemicals substances are used to make the prints appear more clearly. One method is to gently spread a powder onto the print, and then remove the excess powder; the remaining powder will typically adhere to the oils in the print, and reveal their pattern in a way that is more visible. If a print is laid down on a very light surface, a white powder is typically used, as it contrasts well with the dark background. Conversely, if there is a light or transparent background, a dark powder is used. Fingerprints can be also developed by other more advanced techniques, utilizing chemicals that may react to the oils in a latent print or chemicals that may emit light under certain circumstances.

Once a latent fingerprint has been found and developed, it can be photographed or lifted. Lifting a fingerprint is the action in which the developing agent, or powder that has been used to reveal the print, is lifted off the original print with a sticky surface, such as tape, and deposited on a mobile card for transportation and future reference. Lifting prints instead of simply photographing them can be useful when you wish to examine a print in greater detail at a later date or in a different location, such as a laboratory where more advanced techniques could be utilized to analyze the print.

Plastic prints are prints that have been imprinted into a soft medium so as to preserve the three dimensional shape of the original friction ridges. Plastic prints may be left in substances such as soft clay, wax, or putty. This type of print is considerably more rare then a latent print.