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Fingerprint Fuming

In this experiment using superglue, students will explore a simple fuming technique used by forensic scientists to reveal invisible fingerprints.

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 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.

Every fingerprint is unique, but there are certain patterns that can be observed which many prints have in common. Interestingly, even fingerprints from the same individual can vary slightly from finger to finger!

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.

Fingerprints leave behind traces of sweat and oils on surfaces that are not always visible or recoverable by dusting powder. In these cases, a "fuming" technique is used. This technique was developed in Japan in 1977, where Fuseo Matsumura, a hair and fibre expert at the Saga Prefecture Crime Laboratory of the National Police Agency used microscope slides to examine trace evidence that he mounted using superglue. One day, while working on a case, he noticed a fingerprint developing along the side of the glass slide. He presented his finding to a colleague, Masato Soba, who eventually developed superglue fuming.

Cyanoacrylate is a substance in superglue that, when heated, releases into the air as a gas. This gas is attracted to the sweat and oils excreted from fingers and crystallizes to leave behind a white residue that reveals the fingerprint. This processed print can then be lifted and analyzed.

Teacher tip: Use superglue in a well-ventilated area. Superglue can bond skin and eyes in seconds, so be sure to review the safety directions provided on the packaging before starting this activity.

Objectives

  • Explain how invisible (latent) fingerprints are developed and analyzed through chemical means.

Materials

  • Per Demo:
    a drinking glass (or other smooth, non-porous object)
    warm water
    shallow paper cup
    superglue
    aluminum foil
    heat lamp (heat bulbs available at hardware or pet stores)
    large, sealable plastic bag
    pie tray

Key Questions

  • What is the advantage of fingerprint fuming over dusting for fingerprints?

What To Do

  1. Create a latent fingerprint. Rub one finger along the side of your nose to make it oily and then press your fingertip to the side of the glass. (Oily or sticky fingers leave the best prints.)
  2. Fill a shallow paper cup with warm water.
  3. Place the cup and the glass with the latent print in a metal pie tray.
  4. Make a small bowl using a piece of aluminum foil, and squeeze in 4–6 drops of superglue. Place the bowl next to the object with the print.
  5. Place the pie tray and all its contents into the large bag and seal it tightly.
  6. In a well-ventilated area, place the bag beneath a heat lamp and let it sit for 15–25 minutes. Do not open the bag. The cyanoacrylate will evaporate into a gas and react with fingerprint’s residue.

Teacher Tip: Monitor the evidence. If left for too long, the fingerprints will overdevelop and the spaces between the ridges will fill in, obscuring the pattern.

  1. Once the prints have developed, remove the tray from the sealed bag and pull out the object carefully. A white residue print should be fairly visible on the glass.

Extensions

  • Compare this chemical method to physically lifting fingerprints, as in the resource activity Finding Fingerprints.
  • Test several surfaces of various textures and shapes and compare the advantages of each method.