Fingerprinting: A Lesson on Classification

fingerprint image fingerprint image

  This lesson developed by Reach Out!

  Recommended Age Groups: Later Elementary or Middle School


Guiding Question:

Can we invent a way to classify fingerprints?






  • Fingerprints can be classified by pattern types, by the size of those patterns, and by the position of the patterns on the finger.


  • Observing
  • Comparing and contrasting
  • Classifying


  1. 3x5-inch index cards, at least two per participant
  2. pencils and a sharpener
  3. transparent tape; 3/4-inch is better than 1/2-inch
  4. good lighting
  5. hand magnifiers—nice to have but not essential
tented arch image
whorl image


There are three methods you can use for taking prints:
  1. Not recommended: actual rubber-stamp ink pads—too much damage to clothing and surroundings likely

  2. Easiest and cheapest: rubbing pencil all over a small area of paper or index card to make an “ink” pad, pressing fingers onto the penciled area, lifting prints from fingers with transparent tape, and sticking tape to white index cards for reading

  3. High-tech, neat, and not too expensive: using purchased Identiprint materials.

    Identiprint is a commercial system used by retail merchants to put customers’ thumbprints on the backs of their checks without making an inky mess. Special “ink” pads and self-stick labels take a dark, clear print without leaving any visible residue on the thumb. I found supplies by searching the Web for “Identiprint.” A dealer took a telephone order for a roll of 500 labels and a dozen pads, at a cost of less than $35 in 10/97, which I received some ten days later. You may also ask a high-volume retail merchant near you to donate a small supply for classroom use. Experimentation has shown us, however, that the pencil method is actually easier to use—if harder to read.


Room Preparation

Very little: have desks or tables to work at and good lighting

Safety Precautions

None—unless you choose to use regular ink pads! In that case, have soap and water and washcloths on hand for clean-ups and expect a mess, as ink will get onto faces, clothing, and surfaces. Hydrogen peroxide may help to save clothing.

Procedures and Activity


Ask the guiding question: Can we invent a way to classify fingerprints?

If you want to use fingerprints to solve crimes, you must have a way to describe and sort and find prints that are similar to the one you find at a crime scene. The FBI has over 200 million prints on file; they can’t look through every single one to find a match!

Today we are going to look at some of our fingerprints and see how we might sort them into categories, just as fingerprint specialists do.


  1. Divide participants into groups of 2-6

  2. If using graphite pads, have everyone rub a pencil over the central part of an index card until it is covered with graphite.

  3. Give everyone another card for recording his/her prints and have them write their names on the lined side and turn it over.

  4. If using Identiprint, put two stickers on each card.

  5. Each participant will be making prints of the index finger and the middle finger of the same hand. Begin by asking who is right- or left-handed and tell them to use that hand.

  6. Note to participants that they want to make prints not of their fingertips but of the pads of their fingers, near the joint crease, because that is where the most interesting patterns are.

  7. If using Identiprint, printmaking is best done with a partner: Roll the pad of your finger very gently on the “ink” pad and then let your partner roll it slowly and very gently on the label. This is most easily done right at the edge of your table or desk. You do not need to press hard at all; if you do, you will get a black smudge with very little readable pattern. You can do the whole procedure yourself, but it usually comes out clearer with a partner’s help.

  8. If using graphite pads, press and roll your finger firmly on the penciled area, then stick a short piece of tape to the finger pad area, pressing down thoroughly, remove the tape and press it onto your print record card.

  9. Immediately label your print “L” or “R” for left or right hand and “I” or “M” for index or middle finger.

  10. Repeat procedure for the second finger. Do it over until you get two good prints.

  11. After all prints are made and labeled, have partners in each group compare their prints for similarities and differences.

    Note that, while scars, such as the white line on one of the sample prints in this lesson, are the easiest patterns to see, they cannot be used either for classification or identification. They are not unique in the way that ridge patterns are, and they also change over time—making them unreliable for these purposes.

  12. Divide the participants up by patterns, either grouping them physically or grouping their cards by pattern.

  13. Ask how you might look most efficiently for a particular pattern. For example: “In which of these groups would I look for a loop that leans to the left? Would it make sense to look through the whorls?”

  14. Which is the most common pattern? You may wish to graph results, or to figure fractional or percentage representation of each type.

left loop image     radial loop image     right loop image


Closing - Original Question

  Ask again:

  1. How can fingerprints be classified?
  2. How would classification make it easier to match one print against a database of many?

Look for evidence of a plan to search systematically: for example, to look through the left-leaning loops with eight ridges that are close to the finger joint.

Final Note: Fingerprints are a very personal kind of information; let participants take their prints home with them.

Extension Ideas

If you have time, there are many ways to further investigate both fingerprints and classification.

There are many sites on the Web related to fingerprinting. Here are a few:

Careers Related to Lesson Topic

Find information from the Dept.of Labor on protective services occupations:

Prerequisite Vocabulary

To sort into groups by likenesses and differences

Present and not able to be seen but capable of becoming visible. Used to describe fingerprints that are not visible until they are dusted with chalk or other powders, or until they are lit with a laser

Capable of being seen by the eye without help

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