Mystery Science, Part V: Fingerprints

Now you turn your attention back to the glass, but this time it is to see if there are any fingerprints on it which might point to the criminal. But before you begin the analyzing of the fingerprints in our Science Mystery, it might be beneficial for your students to learn about fingerprints in general. If your students just try to identify the prints without the background, it is easy to make mistakes, not knowing what differences to look for. Also, if you have some discussion, it is helpful to have a common terms to use in discussing the differences.

Making Prints

Let's make fingerprints from your students to analyze. There are two ways to make fingerprints at home. The first is the graphite method. For this method, hold a pencil at an angle on paper and fill a small area with graphite.

Roll the edge of one finger over the shiny graphite, making one or two passes. Good technique demands including the entire fingertip, edge to edge and down to the area of the first joint. Keeping the paper at the edge of the table will make this easier.

Have another person pull 2 – 3 inches of tape, while only touching the ends and keeping the sticky side up. Roll your graphite-covered fingertip onto the tape.

Tape this piece of tape to an index card or piece of white paper.

The second method uses an ink pad. You roll finger in the same way as with the graphite method over the ink pad. Roll the inked finger carefully over the index card or white paper. We found the graphite method made the most reliable prints, but you can experiment and see what works best for you.

Classifying Prints

There are three basic types of fingerprints, that all others are based on. You can show these to your students so that they can classify their prints.

Whorls have circles that do not exit on either side of the print.

Arches have lines that start on one side, rise and exit on the other side of the print.

Loops have line that enter and exit on the same side of the print.

 Classifying Their Own Prints
Your students will need to decide which group most of the lines are most like. There may be some disagreement over which group a fingerprint will fit in. Some of the fingerprints that do not fit easily into the three categories are sometimes put into a fourth category called "mixed." Go ahead and present the fourth category of "mixed" only after your students have considered all other options. Introducing this new category too early often results in students placing all hard-to-classify prints in it.

Now, that your students have classified their own prints, use a "fingerprint formula." A fingerprint formula is the list of the print classifications for a hand, from thumb to pinkie. (For example, a hand that has fingers of loop, arch, arch, whorl, loop has a formula of:  l-a-a-w-l. Have your student write his fingerprint formula at the bottom of his fingerprint sheet.

Now that you have some experience with analyzing fingerprints, let us look at Mr. Body's glass in our mystery.

If you would like to set up your own experiment, click here.

If you would like to follow along with our experiment, click here.