On the palmar and plantar portions of the hands and feet, each person has a unique and permanent (barring scarring or injury) arrangement of ridges and furrows, called friction ridge skin. You can think of this skin like the rubber portion of a stamp.
The term "latent" means "hidden". Latent prints are most commonly fingerprints or palm prints that are collected from a crime scene. Latent prints usually need to be processed or developed with a chemical or physical developer in order to be visible to the naked eye.
Latent prints can be left by simply touching an object in a crime scene. The ridges of the hands and feet are composed of sweat pores, but other portions of the body, such as the face, are composed of a variety of glands and pores, including oil glands. Because of this, the ridges of the hands accumulate sweat as well as oil, and these can be easily transferred quite routinely. Anything that accumulates on the ridges of the finger can be transferred and left behind in the same formation as the fingerprint ridges.
To use the stamp analogy once more, think of your finger as the stamp and any accumulated substances (sweat, oils, and various other substances) that it acquires as the "ink". When a stamp is placed on a surface, the ink is left behind in whatever pattern the stamp holds. Similarly, when a person places his/her hand on a surface, any accumulated substances will be left behind in the pattern of the ridges.
In order to view latent prints, many times a processing technique must be used. Listed here are a variety of processing techniques that can be used including (but not limited to):
× Cyanoacrylate/Superglue (CA) Fuming
× Black Powder
× Dye Staining
× Small Particle Reagent (SPR)
× Leucocrystal Violet (LCV)
× Amido Black
Some examples of latent prints that have been processed with a few of these techniques are picture below.
Figure 1: Example of ridges and furrows.*
Figure 2: Anatomy of the friction ridge areas of skin.*
A) Accumulated fat. B) Sweat gland. C) Sweat duct.
D) Mucous Layer. E) Epidermis - outer skin.
F) - G) Pores. H) - I) Friction ridges.
J) Furrow. K) Dermis "inner" skin.
Figure 3: Examples of processed latent prints.
(top left) LCV; (bottom left) SPR; (middle) Indanedione;
(top right) Acid Yellow; (bottom right) CA fumed