Dusting for Fingerprints

Hard surfaces often show fingerprints when dusted with a very fine powder.

Materials:

• Microscope slide (or other smooth, flat object)
• Fingerprint powder or any fine powder (such as talcum powder, cornstarch, or cocoa powder)
• Fingerprint brush (or any small brush with very soft bristles)
• Clear tape

What to do:

1. Touch a microscope slide with your finger a few times to leave prints. (If you want, use lotion on your hands for more obvious prints.) Set the slide on a piece of paper before dusting, for easier cleanup.
2. Sprinkle a little bit of powder on the microscope slide, then gently swipe off the excess powder with the soft brush, being careful to leave the fingerprint intact. This may take some practice to get right.
3. Stick a piece of clear tape over the fingerprint firmly, and then lift it up; the print should adhere to the tape. You can then stick it to contrasting paper to maintain a record of the print.
4. After you become proficient with dusting a slide, try to test other surfaces like doorknobs or faucets.
5. See if you can identify any of the prints you develop. To do this, take the prints of your family members and compare the known prints with the "mystery" prints. Color a couple square inches on a piece of paper with a pencil, have a family member rub their finger on the square to pick up graphite, then have them press their finger down on the sticky side of a piece of tape. Stick the tape to a white sheet of paper and label whose print it is. Compare the known prints to a print you lifted around the house using the procedure on our Fingerprint Analysis Sheet.

What's happening?

Oils from your finger left an impression of your prints on the slide. When you brushed the powder off the smooth slide, some of it stuck to the oils, allowing you to see the patterns.

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