Taking Fingerprints

People have noticed the subtle differences in the fingerprint patterns for hundreds of years. Centuries ago, Chinese and Japanese emperors signed papers with thumbprints to make them authentic. But it wasn’t until the late 1800s that fingerprints were used as evidence to link a suspect to a crime. The first step in understanding fingerprints-and fingerprinting-is to examine your own.

Materials
- magnifying lens
- ink pad
- several sheets of white paper
- marking pen
- pencil
- transparent tape
- helper

Procedure
1. Look at your fingerptips through the magnifying lens and examine the patterns on your skin. These are your fingerprints. Can you describe them in words?
2. Make a set of your fingerprints. There are two easy ways to do this.

Method I
a. Press one finger at a time into the ink pad, being careful not to get your fingers too wet.
b. Have your helper make your fingerprints by holding your hand steady and pressing and rolling your fingers one at a time onto a clean sheet of white paper. Be careful not to smudge the prints.
c. Use the marking pen to label each print with the name of the finger from which it camel thumb, index finger, middle finger, ring finger, pinkie.

Methode II
a. Rub the pencil point back and forth many times on a clean sheet of white paper to make a small dark area of pencil-lead dust.
b. Press one finger at a time into the dust. You may need to rub the pencil point again to get more dust for each fingerprint.
c. Have your helper place the sticky side of a piece of transparent tape on each dusted finger.
d. Tape the prints to another clean sheet of white paper.
e. Use the marking pen to label each print with the name of the finger from which it came.

3. Examine both types of fingerprints with a magnifying lens.

More Fun Stuff to Do
Using either methode. Create a complete set of fingerprints for each of several helpers. Use one sheet of paper for each set, and label the prints so that you know which fingers and which person they came from. Next, have each helper make a fingerprint on separate sheet paper. Do not label these prints. Choose one of the sheets of paper at random. Using your labeled sets of fingerprints, try to figure out whose fingerprint it is. What can you do to make the task easier?

Ask an adult arrange a trip to your local police station to observe how the police take fingerprints. How do their methode compare to the two methods you learned?


Explanation

The skin on the palms of our hands (and the soles of our feet) is covered with tiny raised lines, called friction ridges. These ridges allow people to pick up and handle objects easily. Each person, even an identical twin, has a totally unique pattern of ridges on his or her hands and feet. And for each person, the pattern on each finger or toe is unique and different from the pattern on every other finger or toe.

A fingerprint is an impression of these ridge patterns transferred to a surface. Fingerprints occur because glands in our hands and feet secrete liquids, mainly sweat and oils. These liquids leave the patterned mark of our fingerprints on almost everything we touch.

There are three ways that fingerprints are valuable as evidence. First, fingerprints can confirm the identity of a person. When a criminal is taken into custody, it is a fairly simple task to take his or her fingerprints and cross-check them against other prints. This will prove who the criminal is and determine whether he or she has a criminal record or whether he or she is wanted by the police.

Second. Fingerprints can be used to compare a suspect in custody with fingerprints left at the scene of a crime.
Third, forensic scientist can compare fingerprints left at the scene of a crime with those of a known criminal whose fingerprints are on record.