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Fingerprint Fun

A fingerprint is a mark left behind after the ridges on the fingers, hands, toes or feet touch an object. In this activity, students make a set of direct fingerprints using two different techniques and learn to identify their own friction ridge patterns.

Dactyloscopy (fingerprint identification) is useful to forensic scientists when they compare two fingerprint samples to determine whether or not they came from the same person. Governments around the world have used fingerprints as an identity marker for more than a hundred years.

Although manual identification of fingerprints is a time-consuming process, today, there are major databases and programs, such as the Automated Fingerprint Identification System (AFIS), that are used by police agencies to scan fingerprints for a match in as little as two minutes. 

Fingerprints are what we call the pattern of ridges on the fingers that provide a rough surface that helps create the friction needed to pick up a baseball or hold onto a pencil; they are also know as "friction ridges". These ridges are formed before birth. By the time a fetus is 11 weeks old, the first, gentlest ridges have formed on its fingers. One of the deepest layers of skin pushes upwards, making ripples in the layers of skin above it. By the time a baby is born, there are seven layers of skin, and fingerprint ridges ripple through the top five layers. 

Baring loss of a finger tip to injury, or intensive scarring, the friction ridge pattern of individuals will constantly re-grow the same as their skin re-news throughout their lives.

Fingerprints have three main classes of friction ridge: the arch, whorl and loop.

  • Arches have lines that start on one side and rise and exit on the other side of the print. They look like a hill.
  • Loops have lines that enter and exit on the same side of the print. They look like an upside-down U.
  • Whorls have circles that spiral and do not exit on either side of the print. They look like a bull’s eye.

Every fingerprint is unique, but there are certain patterns that can be observed which many prints have in common. Explore student's fingerprints in this activity and see what classes of ridge patterns they each have. Interestingly, even fingerprints from the same individual can vary slightly from finger to finger!

Objectives

  • Develop and analyze their own and others’ fingerprints through physical means.

Materials

Key Questions

  • How are your fingerprints different from your friends’?
  • Where do the pattern lines begin and end?
  • Which direction do they face?
  • Why do we have fingerprints?
  • How are they formed?
  • Why are fingerprints important to forensic scientists?
  • Can a person change or remove his or her fingerprints?

What To Do

Part 1: Fingerprinting using graphite

  1. Each group receives a #2 pencil, piece of paper, clear tape, Fingerprint Pattern Identification Sheet.
  2. Each student receives the Fingerprint Identification Template to record their prints.
  3. Rub a small, black patch of graphite onto a piece of paper using the pencil.
  4. Rub one finger across the graphite patch. Use the front pad of the finger, not just the tip.
  5. Lay a piece of tape over the blackened finger, then remove it cleanly to lift the fingerprint directly from the finger.
  6. Stick the tape on the Fingerprint Identification Template in the appropriate box.
  7. Repeat for each finger on each hand. Afterwards, wash your hands so you don’t contaminate the “evidence.”
  8. Once the fingerprint handouts are complete, you can then examine the ridge patterns of your fingers, using a magnifying glass and a Fingerprint Pattern Identification Sheet to classify your prints.

Part 2: Fingerprinting using ink

  1. Each group receives an ink pad, and each student receives a template to record their prints.
  2. Press a finger gently into the ink-soaked fabric using the front pad of the finger, not just the tip. Using too much ink or pressing too hard into the ink pad will cause the print to smudge, and you will not be able to see the patterns.
  3. Press the inked finger onto the second Fingerprint Identification Template, by rolling the finger from left to right. This is a technique used by experts to get a thorough print.
  4. Clean the finger and move onto the next, until all fingers and thumbs have been printed.
  5. Once the fingerprint handouts are complete (and, if necessary, dry), use a magnifying glass and the Fingerprint Pattern Identification Sheet to examine the ridge patterns and classify the prints.

Teacher Tip: Inky fingers can make a mess! Keep a package of baby wipes to help students wipe off as much ink as possible.

Extensions

  • Students can enlarge a fingerprint simply by placing the print on a balloon and inflating the balloon. This method works best when you use a permanent marker to blacken the finger and create the print.