How Do Fingerprints Differ?
The skin’s surface is marked by a series of fine lines and ridges which deepen with age. The pattern on the tips of the fingers is peculiar to each individual and is used as a means of identification. In fact, the ridges of the skin on the lower finger joints and the toe prints are also unique, as are palm prints and foot prints. But fingerprints are by far the most simple and effective identification method.
Each ridge of the outer skin (epidermis) is dotted with sweat pores and anchored to the inner skin (dermis) by a double row of peglike objects called papillae. Injuries which affect the epidermis do not alter the ridge structure, and the original pattern returns in the new skin. If the papillae are destroyed, however, the ridges will disappear.
There are five general pattern shapes or types: the arch, the tented arch, the radial loop, the ulnar loop and the whorl. Whorls are usually circular or spiral, arches are shaped like a mound or hill and tented arches have a spike or “steeple” in the centre. Loops have concentric hairpin-shaped ridges and are divided into “radial” and “ulnar” to denote their slopes in relation to the radius and ulna bones of the forearm. Ulnar loops slope towards the little finger side of the hand and radial loops slope towards the thumb.
The pattern on our fingertips remains the same from birth until death, barring deliberate or accidental destruction of the papillae. Fingerprints therefore provide a positive identification, and the practice of fingerprinting known as (dactyloscopy) is an essential part of police procedure. Fingerprint identification, or hand print identification, is the process of comparing two instances of friction ridge skin impressions, from human fingers or toes, or even the palm of the hand or sole of the foot, to determine whether these impressions could have come from the same individual. The flexibility of friction ridge skin means that no two finger or palm prints are ever exactly alike in every detail; even two impressions recorded immediately after each other from the same hand may be slightly different.
Fingerprint identification, also referred to as individualization, involves an expert, or an expert computer system operating under threshold scoring rules, determining whether two friction ridge impressions are likely to have originated from the same finger or palm (or toe or sole). An intentional recording of friction ridges is usually made with black printer’s ink rolled across a contrasting white background, typically a white card.
Friction ridges can also be recorded digitally, usually on a glass plate, using a technique called Live Scan. A “latent print” is the chance recording of friction ridges deposited on the surface of an object or a wall. Latent prints are invisible to the naked eye, whereas “patent prints” or “plastic prints” are viewable with the unaided eye. Latent prints are often fragmentary and require the use of chemical methods, powder, or alternative light sources in order to be made clear. Sometimes an ordinary bright flashlight will make a latent print visible.
When friction ridges come into contact with a surface that will take a print, material that is on the friction ridges such as perspiration, oil, grease, ink or blood, will be transferred to the surface. Factors which affect the quality of friction ridge impressions are numerous. Pliability of the skin, deposition pressure, slippage, the material from which the surface is made, the roughness of the surface and the substance deposited are just some of the various factors which can cause a latent print to appear differently from any known recording of the same friction ridges. Indeed, the conditions surrounding every instance of friction ridge deposition are unique and never duplicated. For these reasons, fingerprint examiners are required to undergo extensive training. The scientific study of fingerprints is called dermatoglyphics.