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Fingerprint
A fingerprint is an impression made by the ridges on a finger’s surface. These ridges, called “friction ridges,” are raised portions of the skin, found on the fingers, toes, and hands. Humans have friction ridges on these areas of their skin to help grip objects. The ridges may also help improve in texture perception, because they amplify the vibrations that are caused when a fingertip brushes across a surface.
The patterns in friction ridges are unique to each individual and they do not change over time. Even identical twins that have the same DNA do not have identical fingerprints. For this reason, fingerprinting is an effective means of identification.
Humans leave fingerprints when they touch things because of secretions from the eccrine glands. These glands are located in the friction ridge skin, and their secretions consist mainly of water. Any material on the finger’s surface also contributes to the print – such as sweat, oil, grease, or ink. When fingerprints are made for identification purposes, the subject usually applies black ink to his or her finger, and then makes a print on a white card. Today fingerprints can also be recorded digitally, in a method called Live-Scan.
Fingerprint identification is the process of comparing friction skin ridge from fingers to determine if the impressions are from the same person. Toes or the palms of hands can also be used for identification, since they also have unique friction ridge patterns. In the identification process, typically a “known print” and a “latent print” are compared. A known print is the intentional recording of a fingerprint for comparison purposes, while a latent print is an invisible fingerprint found on the surface of an item.
In addition to known and latent prints, there are also two other classifications of fingerprints: patent prints and plastic prints. Patent prints are fingerprints that are visible to the human eye. For example, a patent print might be a fingerprint made with blood, dirt, or ink, left at a crime scene. Plastic prints are three-dimensional prints left in a material that retains the actual shape of the finger’s friction ridges. Plastic prints can be found in melted candle wax, in clay, or in thick grease deposits on car parts. Examples of plastic prints have been found on ancient artifacts, such as on Babylonian clay tablets and seals, and on Minoan, Greek, and Chinese pottery.
Since the late 1800s, police around the world have used fingerprints to identify suspected criminals and the victims of crimes. Usually to do this, investigators have to make latent fingerprints at a crime scene visible. The best way to do this depends on the type of surface involved. In most cases, you need to use a ‘developer,’ which is a powder or chemical reagent. When added to the print, it produces the visual contrast needed to see the print.
The effectiveness of a particular developer depends on the presence of organic materials or inorganic salts. Fingerprints consist usually of water with small amounts of amino acids, chlorides, and fatty components. The reactive organic material in this – usually urea or amino acids – will change color usually with the addition of a simple powder. Sample fingerprint reagents include Ninhydrin and Diazo-fluorenone.
The use of fingerprints extends back thousands of years. In Babylon from 1885-1913 B.C.E., fingerprints were sometimes used as substitutes for signatures on legal documents. By 246 B.C.E., Chinese officials used fingerprints in the clay seals that sealed documents. Japan also adopted the practice of sealing contracts with fingerprints by 702 C.E.
Fingerprints were also taken from criminals in both ancient Babylon and China. The Babylonian king Hammurabi (1792-1750 B.C.E.) had a law mandating that officials fingerprint people who had been arrested. In China beginning around 300 C.E., handprints could be used as evidence in trials relating to theft.
The modern study of fingerprinting began in the 17th century. In 1684, Nehemiah Grew, an English physician, botanist, and microscopist, published a paper on the ridge structures of the skin. A century later, in 1788, German anatomist Johann Christoph Andreas Mayer identified that the fingerprints of every person are unique. It was in the 19th century that fingerprinting was first used extensively for identification purposes. In 1858, Sir William James Herschel initiated fingerprinting in India. In 1892, Sir Francis Galton published the first comprehensive guide to fingerprint analysis and identification. This paved the way for the founding of the first United Kingdom Fingerprint Bureau in 1901. The practice made its way to the United States in 1902, when Dr. Henry P. DeForrest used fingerprinting in the New York Civil Service.
The validity of fingerprint evidence has recently been challenged, because of the subjective nature of matching. Although the error rate is low, significant errors have been made in the past.
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