Fingerprinting

  

History

Fingerprinting is one of the most commonly known methods of investigation in forensics. Fingerprint identification has been used for over 100 years, and in all the billions of humans, no two fingerprints have ever been the same. Fingerprints were used as far back as the ancient times, as in ancient China and 14th century Persia, when thumb prints were on seals of important documents. In 1686 ridges, loops, and other patterns were noticed on fingerprint, these patterns were first analyzed under a microscope in 1823. In 1858 it was realized that no two fingerprints are the same, by Sir William Herschel, who used fingerprints on the back of contracts. Fingerprints were first used in America when Gilbert Thompson used his own fingerprints to prevent forgery on a document. By 1892 fingerprints were discussed as a reliable source of identification, and the first criminal fingerprint identification was collected. By the 1900s it was possible to put fingerprints into a computer system and quickly identify any matches.

Types of Fingerprints
There are three different types of fingerprints: direct, plastic and latent.
Direct Fingerprints (Patent Fingerprints)
 
These are visible prints that occur when a foreign substance is on a finger, and that substance gets pressed onto a smooth surface by the finger. The foreign substance collects dust particles, which adheres to the ridges on the fingerprint, making them easily identifiable.



Plastic Fingerprints
These are also visible prints, but they are impressed into a soft surface such as clay or chocolate. These types of fingerprints can also be found on surfaces with wet paint, or any other surface that soften when hand held. These prints are good to use because they need no extra enhancement to be properly viewed.







Latent Fingerprints
 
 These are prints that are usually invisible to the naked eye. They result from perspiration that is derived from sweat pores in fingers. Because of this sweat, and other oils on fingers, when fingers touch a surface a film of these substances is left on the surface, with the pattern of the fingerprint. These types of fingerprints must be enhanced to properly view, but can still be a valuable source of identification.



How to Obtain Fingerprints (Techniques and Chemicals Used for Different Surfaces)
There are different methods used to obtain fingerprints depending on the surface (hard, porous, smooth and nonabsorbent).
Hard, Smooth, Nonabsorbent Surfaces

These surfaces, such as tile, glass, or painted wood, require powder to find the prints.  For dark surfaces use light powders, and for light surfaces use carbon or charcoal powder. Fluorescent powder can also be used although it is only visible under blacklight. For this method apply the powder to the area with the fingerprint and gently dust away the excess, revealing the fingerprint. This print, now visible, can be lifted using tape.




 
Soft and Porous Surfaces

These surfaces, such as cardboard, paper and cloth require chemicals to find any fingerprints. Iodine is a chemical used in a fuming process to photograph fingerprints. Ninhydrin is used in a 6% solution, it is dissolved in ethyl alcohol or acetone and sprayed onto the area with fingerprints. In around an hour the print will show up a dark purple color. A 3% solution of Silver Nitrate can be used as well, it is applied to the fingerprint  and then an ultaviolet light is used to show the prints (they will be reddish brown). This method should only be used as a last resort though, because it causes the other chemical methods to become ineffective.

We did a mini lab lifting fingerprints. We lifted them from both dark and light surfaces, so we used both carbon powder and white powder.


In class we fingerprinted our own hands to analyze the patterns. This is shown below.

Patterns
Fingerprinting is not as easy as putting together two prints, as there are millions of prints in the world. Each individual print can be characterized by certain patterns.
These patterns include:
Arches (5% of Fingerprints are Arches)
    
Plain Arch                       Tented Arch

Loops (30% of Fingerprints are these)

 
Radial Loop                        Ulnar Loop


Whorls (65% of fingerprints are these)

 

Plain Whorl

Central Pocket Whorl

  

Double Loop Whorl

Accidental Whorl