Fingerprinting

Fingerprint: An impression on a surface of the curves formed by the ridges on a fingertip

History of fingerprinting:

In ancient civilizations, a criminal was marked as a criminal through branding or maiming. The thief would lose the hand that was used to commit the thievery.

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. In 1686 a man called Malpighius  described the ridges on fingerprints, but stopped at that.

Then in 1823 J.E. Purkynie discovered it was possible to classify fingerprints, and that’s when fingerprinting began. Around 1858 Sir William Herschel demanded labourers to sign contracts with fingerprints in India. The first known use of fingerprints in the United States was by Gilbert Thomson of the U.S. geological Survey in New Mexico in 1882. He used his own fingerprints on a document in order to prevent forgery. Between the years 1901 and 1910 many countries began using fingerprints, and soon, in 1924 in America, the Identification Division from the FBI started.

Four types of fingerprints:

Latent- A fingerprint "image" that is left on a surface that was touched by an individual. Left by the surface contact with the friction ridges, usually caused by the oily residues produced by the sweat glands in the finger. Not apparent to the human eye.

Patent- Known as visible prints that is obvious to the human eye. You can notice these with the naked eye because they are left with something else. Such as: Blood, dirt, ink, or grease on the finger come in contact with a surface and leave a friction ridge impression.

Plastic- A friction ridge impression left in a material that retains the shape of the ridge detail. Usually left in soft pliable surfaces, such as clay, wax, paint or another surface that will take the impression. They are visible and can be viewed or photographed without development.

Techniques/ Chemicals used to develop prints:

Black powder

On hard, smooth, and nonabsorbent surfaces such as: mirrors, tile, glass, and painted wood prints are developed with powder. Black powder which is composed of black carbon or charcoal is applied to light colored surfaces. Gray powder which is composed of aluminum dust is used on dark colored surfaces. Fluorescent powders can also be used to develop latent prints, which will fluoresce under ultraviolet light.

 

Silver Nitrate



On soft and porous surfaces such as: cloth, paper, and cardboard are developed by iodine fuming, silver nitrate, and super glue. Iodine fuming is where the contaminated material is placed in an enclosed cabinet. While in the cabinet the vapors will then combine with the components of the latent print and make it visible to the human eye. 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. In the super glue the cyanoacrylate fumes bond to the oils on the surface of the object making the print permanent.

Classification of Fingers:

Arches are found in about 5% of fingerprint patterns. There are two types of arches plain and tented.

Tented arch

Plain arch

Plain arches have an even flow of ridges from one side to the other of the pattern, they contain no up thrusts and the ridges enter on one side of the impression, and flow out the other with a rise or wave in the center.

Tented arches are the opposite of plain arches they do contain up thrusts in the ridges near the middle that arrange themselves on both sides of a spine or axis towards which the adjoining ridges join and appear to form tents.

Loops:



Loops occur in about 60-70 % of fingerprint patterns. The ridges make a backward turn but do not twist depending on how they twist they can be determine as radial or ulnar loop.

Radial loops are named after the radius which is a bone in the forearm that joins the hand on the same side as the thumb. The flow of the pattern in radial loops runs in the direction of the radius toward the thumb.

Ulnar loops are named after the ulna which is a bone in the forearm. The ulna is on the same side as the little finger and the flow of the pattern in a ulnar loop runs in the direction of the ulna toward the little finger.

Whorls:



Double loop whorl





Plain whorl



Accidental whorl

Central pocket loop whorl

 

Plain whorls consist of one or more ridges which tend to make a complete circuit with two deltas.

Central pocket loop consist of at least one re-curving ridge. Central pocket loop whorl ridges make one complete circuit which may be spiral, oval, circular or any variant of a circle.

Double loop whorls there are two separate loop formations. In each of these formations, there are two entirely separate and distinct sets of shoulders and deltas.

Accidental whorl is a pattern which possesses some of the requirements for two or more different types of other patterns.

People of African descent tend to have plenty of arches. People of European background have frequent loops. While Asians/ Orientals have high frequency of whorls.

Lifting techniques:

There are hinge lifters, rubber lifters and cellophane tape.

Hinge lifters- Are placed on the print and pressed down evenly. The lifted print is covered with the hinged cover and is protected from scratches and dirt. Using a roller can sometimes help to smooth the cover to avoid bubbles. An image of the fingerprint is obtained just as it was found.

Rubber lifter- The plastic cover should be carefully removed. The adhesive side of the tape should be applied to the powdered print, and pressed down evenly. Then the tape is peeled from the surface in one smooth, even motion. The plastic cover is replaced on the tape over the lifted print to protect it. A negative image of the fingerprint is obtained.

Cellophane tape- The print area is covered about an inch beyond in the other direction. The tape is gently rubbed over the print. After the tape is firmly in place, the print is lifted by pulling the roll gently and evenly away from the surface.