What are fingerprints?
- The impression of the raised portions, or ridges, of the skin
- imprint consists of natural secretions from sweat glands (water, oils, salt) and dirt

How are fingerprints formed?
- formed during the 10th week of pregnancy
- happens in the basal layer – layer in epidermis where new skin cells are produced
- basal layer grows faster than the epidermis (outside) and dermis (inside)
- when the basal layer folds and collapses, fingerprints are formed
Other types of “prints”
- palms, soles of feet, lips

Characteristics of Fingerprints

Loops – 65% of population
- enter from either the right or left and exit from the same they entered

Whorls – 30% of population
- bull’s-eye with two deltas

- plain whorl – 24% - one or more ridges that make a complete spiral; two deltas; if line drawn between two deltas, at least one ridge in inner pattern cut by the line

- central pocket loop whorl – 2% - one or more ridges that make a complete circle; two deltas; if line drawn between two deltas, no inner patterns are cut by the line

- double loop whorl – 4% - two separate loop formations and two deltas

- accidental whorl – 0.01% - has two or more deltas and is combination of two of the other patterns


Arches – 5% of population
- enter from one side and leave from the other with a rise in the middle

- plain arch – 4% - enters one side, rises in center and exits other side without making an angle

- tented arch – forms and angle or may possess a characteristic of the loop patter (like a delta)

Pattern Pictures: http://ridgesandfurrows.homestead.com/fingerprint_patterns.html



Ridge Count
Core – center of a loop or whorl
Delta – triangular region located near a loop
- imaginary line drawn from center of the core to the edge of the delta and the lines in between are counted


Fingerprint Identification
minutiae – unique ridge patterns with small details
- used to positively match a fingerprint
- look at differences between ridges, number of minutiae, and location on a fingerprint
- about 150 individual ridge characteristics on an individual fingerprint

minutiae_patterns.jpg

Types of Fingerprints and Methods of Collection

Patent fingerprints – visible prints left on a smooth surface

Plastic fingerprints – indentations left in a soft material

Latent fingerprints – hidden prints left by the transfer of oils or other body secretions; can be made visible with dusting or using a chemical reaction

Detection_of_Latent_Prints.jpg