What Are Fingerprints?

Fingerprints are made of ridges on the upper skin on hands and feet of all people and some animals. These ridges make lines of different size's and forms, unique to every person. When these parts of the skin come into contact with a surface, a copy of the fingerprint is left behind in a water-based oil. The main component of a fingerprint is sweat, which is mainly water. This will dry up fairly quickly. The other components are solid, and can remain on a surface for a long time. These are amino acids, lactic acid, peptides, glucose, riboflavin, lactic acid, potassium, sodium and several others. This is not the only way a fingerprint can be left behind though. As well as the print being left behind through a water-based oil, the ridges can leave marks in a soft underground such as clay, prints can be left in the likes of dust, or a dirty finger can leave its mark in something else, such as blood or mud. Fingerprints form before we are even born, and they stay the same throughout our lives, not changing. Many believe that identical twins will have identical fingerprints. Though they share the same DNA, their fingerprints will always be unique. A print is made up of a collection of lines and whirls, making up a very unique pattern. It is often wondered just how long a fingerprint can exists after being left on a surface, but there is no answer to that question. Some fingerprints left disappear after a day, and others may last for years.

There are about 7 types in all, each with an infinite number of differences.

Arch – Lines moving in waves from one side to the other.

Tentarch – Similar to arches but with a rise in the middle.

Loop – Lines which come from one side and return in the middle on the same side.

Double Loop – Similar to the loop but with two loops inside.

Pocked Loop – Similar to the loop with a small circle in the turning point.

Whorl – Lines that make circles.

Mixed Figure – Composed with many different figures.

History Of Fingerprinting

Fingerprinting, also known as dactylography, is definitely not a new technique. About 1750 years BC, the people in Babylon used fingerprints to sign their identity on clay tablets. In about the year 220 the Chinese were the first to use ink prints, but then after that fingerprints became forgotten for several hundred years. In 1686 a man called Malpighius. Malpighius wrote describing the ridges on fingerprints, but stopped at that. Then in 1823 J.E. Purkynie discovered it was possible to classify fingerprints, and from there the use of fingerprinting began. In 1858 Sir William Herschel demanded labourers to sign contracts with fingerprints in India, and later in 1877 he suggested taking the prints of prisoners. In 1880 Doctor Henry Fauldspublished a piece on the use of fingerprinting in England, and two years later Gilbert Thompson used thumbprints on cheques to avoid fraud in the USA. Between the years 1901 and 1910 many countries began using fingerprints, and soon, in 1924 in America, the Identification Division from the FBI started.

Methods Of Detecting & Taking Latent Prints

Nowadays fingerprinting is used widely across the world, with many uses. One major use of fingerprinting is in criminal investigations. Something that is commonly carried out at crime scenes is fingerprinting, through different methods. Fingerprints may be found and collected at crime scenes, and later used to link suspects to the scene of the crime.

Fingerprints can sometimes be seen on their own, such as prints on glass. But often they are not visible to the eye, and so methods of making prints visible are used. There are several methods of detecting latent prints.

-Powder And Tape-

Probably the most well-known method of detecting latent prints is dusting for them. A variety of powders are used in dusting for prints, many containing aluminium or carbon. This finely crushed powder is gently applied to a surface, and the minute particles of powder cling to the print residue, making it visible to the human eye. These prints are then lifted using adhesive tape. For dusting to work, the surface that is being dusted must be completely dry and relatively free of other contamination.

-Magna Brush-

This is a magnetic wand that attracts iron. It is dipped in iron dust, and the particles cling to it. This is then used the same as dusting using carbon and aluminium powders. The Magna Brush is also less messy, as any excess iron particles can be easily collected with the Magna Brush. A variety of fluorescent colours are available for this, and some of these powders reflect alternative light sources such as UV and lasers.

-The cyanoacrylate fuming method-

The cyanoacrylate fuming method, also known as the superglue fuming method, has proved to be another very useful way of detecting latent prints. This method was first used by the Criminal Identification Division of the Japanese National Police Agency in 1978. Shortly after this it was adopted in the US, and now it is a commonly used method of detecting prints. Most superglues are methylcyanoacrylate or ethylcyanoacrylate. This reacts with the traces of amino acids, fatty acids, and proteins in fingerprints as well as the moisture in the air, making them visible.

-Ninhydrin-

Another common method of fingerprint detection is the use of ninhydrin. This is sprayed, swabbed or dripped onto the surface. Ninhydrin reacts with the amino acids in the prints, forming a purple or pink compound.

-Iodine Fuming-

Iodine crystals are placed in a glass tube known as a fumer. The examiner then blows into the fumer, causing the transformation from solid to gas. The iodine vapours are emitted from the other end, and if the tube is aimed at a latent print, it will become visible for a short time.

-Silver Nitrate-

Silver Nitrate is a less toxic way of detecting prints on paper. Silver chloride turns black in light, and one of the components of sweat is sodium chloride. The silver nitrate is placed with distilled water and applied to the paper. The paper is exposed to light, and any prints will turn black.

-Amido Black-

Amido Black is a chemical used to develop fingerprints in blood. A fixing agent is first applied to the blood stain, and then amido black is used.

There are other methods of detecting latent prints, most similar to the techniques mentioned above. Some methods even include laser technology. Different surfaces will require different techniques for developing latent prints. For example, when developing a print on paper, Ninhydrin should be used, though powders may work but not as effectively. When developing prints in blood, Amido Black should be used, and powder works best on non-porous surfaces.

When taking fingerprints from people, ink is rolled over the fingers and then the fingers are pressed down on papers or cards. However when it comes to fingerprinting the dead, it does not come so easy. If we are fingerprinting a corpse recently deceased, there is no problem. However if we are dealing with decomposition or mummification where the skin has become hardened and contracted, a special method is required. Usually the fingers are soaked in a solution of glycol, lactic acid and distilled water, softening the finger tissues. If the skin has been wrinkled by the damp, the fingers can be printed by either use of a hypodermic syringe, gently manipulating the fingertips by hand, or removing the finger skin altogether and mounting it to be printed.

Fingerprints found at crime scenes are very rarely fully intact, which means the quality of the print is lower, and can be more difficult to positively match. When multiple sets of prints are being compare, a certain number of characteristic points must be a match. Worldwide there is no set number of how many points must match before it is accepted as a match, but it does differ in some countries. For example, in the Netherlands 12 points are required, whereas in Africa only 7 points are required. It also differs within some countries too. Paris has a requirement of 17 points, whereas the rest of France only requires 12.

Other Uses

Fingerprints are not just used to connect criminals to crime scenes though. When human remains are found, fingerprinting is a very common way of identifying them. Fingerprints are also used for security reasons, such as on certain ID cards and as entrance control at important buildings.

No Prints

In very rare cases some people are actually born without any prints on their fingers, palms or feet. Though this can be a condition people are born with, some people’s ridges degenerate during their lives.

Fingerprint Databases

Automated Fingerprint Identification System, or AFIS, is a database of fingerprints taken and stored in the United States, though other countries such as Canada and the United Kingdom also have their own AFIS. The prints may have been taken for a number of reasons, and the system is used for a variety of purposes, including criminal identification, receipt of benefits, background checks, and receipt of credentials. The machine used to scan fingerprints is called the LiveScan Device. AFIS makes it possible to sift through vast amounts of fingerprints every second, and the computer marks all minutiae (individual characteristics) it recognises. The technician goes over these points the computer has marked, submits the minutiae to a one-to-many search, and the computer gives the results with a percentage of matched minutiae points. A latent print examiner then checks through the possible matches to determine the most likely match.