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STEM Experiment: Little Detective

Ever wonder how detectives find people’s fingerprints at a crime scene? With some simple supplies and techniques, you can have fun with dusting for fingerprints.

Key Concepts

  • Dactyloscopy
  • Latent fingerprints

What you’ll need

  1. A glass or smooth metal surface 
  2. Raw cacao powder or baby powder 
  3. White paper  or black paper 
  4. A small bowl
  5. Clear tape
  6. A fine brush with soft bristles
  7. Dust cloth
  8. Water
  9. Soap
  10. Hand lotion

Instructions

finger print with name written next to it to identify whose fingerprint it is

Fingerprint

  1. Wipe the smooth glass or metal surface that you are using for your experiment very thoroughly with the dust cloth.
  2. Press your finger on a glass or smooth metal surface  (Apply some lotion to your hands before pressing down will help you to see the fingerprint easier)
  3. Pour a little of the cacao or baby powder into a small bowl. White powder is used to dust prints on dark surfaces, and dark powder is used if the print is left on light colored surfaces.
  4. Sprinkle a small amount of powder on the print. You can also blow the powder around a bit to get the print covered as well. 
  5. Gently brush the excess powder off the print Only the tips of the bristles should be covered with powder.( circular dabbing motion)
  6. Use a piece of clear tape and carefully press the tape down onto the surface on top of the developed fingerprint. Peel the tape off and transfer the fingerprint onto a piece of white or black paper (the contrast between the print and the paper will make it easy to see when you put it down).
  7. Write your name on the paper. Then you can identify it later.
  8. Wash your hands thoroughly with warm water and soap. Then, repeat the steps with your friends’ finger see if it looks the same when you compare it to what they have. Can you find whose fingerprint it is?

Scientific Facts

  1. A person’s fingerprints are based on the patterns of skin ridges on the pads of the fingers. These ridges are also present on the toes, the palms of the hands, and the soles of the feet. They develop before birth and remain the same throughout life.
  2. The fingerprints left by people on objects that they have touched can be either visible or latent.
  3. Dactyloscopy, the science of fingerprint identification.
  4. The recovery of partial fingerprints from a crime scene is an important method of forensic science.
  5. The first professional forensic organization is the International Association for Identification (IAI), founded in 1915.
  6. For more than a century it has remained the most commonly used forensic evidence worldwide.
  7. Latent fingerprints are traces of sweat, oil, or other natural secretions on the skin, and they are not ordinarily visible. Latent fingerprints can be made visible by dusting techniques.

Questions you may ask:

  1. How does your friend’s fingerprint of you look compare with the one you made?
  2. Can you Identify whose fingerprint it is?
  3. Try to find the fingerprint on the glass that more than one people touch at the same spot, is it hard to identify?
  4. Could you touch anything in the crime scene and why?