Fingerprints

There are three fundamental principles that fingerprints obey:

1. A fingerprint is an individual characteristic. No two identical fingerprints have
   been taken from different individuals.
2. A fingerprint will remain unchanged during an individual’s lifetime.
3. Fingerprints have general characteristic ridge patterns that permit them to be
    systematically classified.

     The individuality of any fingerprint is based upon its ridge structure and specific characteristics. The special characteristics that make the fingerprint a specific identifying characteristic of each individual is the number of ridges and the approximate location of them. The average fingerprint has 150 individual ridge characteristics. If between 10 and 16 specific points of reference correspond identically, a match is assumed. In court there must be 12 point-by-point comparisons that match.

MATERIALS:

     plastic airline cups or other surface for  fingerprints
     super glue (the larger tubes work better than the tiny tubes in the six pack)
     Ziplock bag large enough for the object with the fingerprints

PROCEDURE:

1. Wipe the cup clean to make sure there are no fingerprints.
2. Rub the underside of your finger on the bridge of your nose or on your temples,
   to pick up extra skin oil.
3. Press the finger onto the cup where you want the print. Be careful not to
    smudge the print.
4. The print should be faintly visible to you at this point. If it is not repeat the
    procedure starting with wiping the cup clean.
5. Place the cup in the ziplock bag. Add about 3 drops of super glue to the bag
    making sure that the drops do not hit the actual fingerprint.
6. In about an hour the fingerprints should be clearly visible in white.
7. Make up fingerprint cards for the students to match. One of the cards should
    be of the same finger as the one on the glass.
8. Have the students compare the fingerprint on the cup with the ones on the
    evidence cards using a magnifying glass.