General Notes
Described below are a number of fingerprinting techniques I use in with my high school students. They work in small groups, and I have one group make "evidence," then exchange it with a different group. They use the appropriate techniques to develop the prints, then match them up with the ten-print cards prepared earlier. We do a different set of methods each semester.
Black powder: useful on glass or other smooth, light-colored surfaces.
Fluorescent powder: used on multicolored surfaces.
Ninhydrin: for developing prints on paper.
Superglue fumes: for finding prints on metal surfaces.
Crystal violet: develops prints on the sticky side of tape.
Iodine fumes: for finding prints on paper.
Preparing the evidence:
Clean a microscope slide in warm, soapy water. Use a grease pencil to mark the slide. Have a student carefully press a thumb in the middle of the slide. Do not roll or slide the thumb while pressing. Record which student leaves this print.
Developing the print:
Procedure
1. Place the evidence on a sheet of newspaper. This will facilitate clean-up afterward.
2. Dip the brush in the powder and lightly dust the microscope slide containing the print. Use only a very small amount of powder. Be gentle when dusting the slide. A swirling motion with the brush works well.
3. If possible, pick up the object that carries the print and tap the edge of the object to uniformly distribute the dusting powder and to remove extra powder.
4. To lift the print from the slide to the index card, unroll about 5Ó to 6Ó of clear packing tape and place the end to the right of the thumb print on the slide and allow the tape to cover the whole print. Slide a thumb over the tape and smooth it down over the print to force out all air bubbles.
5. The print can be removed by pulling up on the roll end of the tape and then placing it on the blank index card in the same manner as the tape was placed over the latent print. Make sure the tape is secure. Cut the tape from the roll.
6. Determine the pattern and identity of the print and record on the data sheet.
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Preparing the evidence:
Use forceps to avoid leaving extra prints on the sample. Cut a piece of a multicolored magazine page, about 3-4 cm square. To leave a print on the magazine page, wipe one finger across your forehead, then apply that finger with moderate pressure to the page. Do not roll or move the finger while touching the paper.
Developing the print:
Use the fluorescent powder and brush the dust the magazine page. Use only a small amount of powder, and dust the page gently to avoid smearing the print. Illuminate the page with the BlueMaxx light and look through the filter to examine the fingerprint.
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Teacher's notes:
Wear gloves while working with this solution, or you will stain your fingers! Mix .63 g ninhydrin crystals in 100 mL acetone. Stir until dissolved. When ironing, place the sample between a folded piece of cotton, such as an old sheet or pillowcase.
Preparing the evidence:
Wear gloves or use forceps to avoid leaving extraneous fingerprints. Cut a piece of white paper, about 3-4 cm square. Wipe a finger across your forehead, then apply the fingertip to the white paper. Again, do not roll or move the finger while pressing.
Developing the print:
When using ninhydrin, always wear gloves!
A. Prepare the "sandwich" papers by cutting two squares of white paper, each about 6-7 cm on a side. Label each paper, along the edge, using pencil, with the word "sandwich."
B. Working over a sink, spray these two papers with the ninhydrin solution until they are soaked. Hold the papers and allow to air dry.
C. Place the evidence between the two sandwich papers, and place flat on the cloth supplied by the teacher.
D. Iron the "sandwich," with the iron on the highest setting, for about 45 seconds, moving the iron back and forth the entire time. Watch the papers carefully to make sure they donŐt burn.
E. Remove the evidence paper and examine the print.
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Preparing the evidence:
Carefully smooth out a piece of aluminum foil, about 3-4 cm square. Wipe one finger across your forehead, then apply that finger with moderate pressure to the foil.
Developing the print:
Use in a well-ventilated area! Allow fumes to dissipate before removing evidence from the chamber! Superglue fumes can irritate lungs and eyes.
1. Make a small cup of aluminum foil. Put seven to ten drops of superglue in this cup.
2. Place the cup in the fuming chamber (this can be an old aquarium, turned upside-down, a lidded box lined in foil, or a chamber made for the purpose). For fastest results, put the cup of foil on a coffee cup warmer or candle warmer. Also, put a cup of warm water in the chamber (note: you will not be able to drink from this cup again!).
3. Put the foil evidence in the chamber, being sure to not let the evidence touch the superglue. (If possible, hang the evidence in the chamber.) Close the chamber and wait about 20 minutes (or 24 hours if the glue is not heated).
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Preparing the solution:
Mix .5 g of crystal violet powder per 500 ml of water (tap water is fine).
Preparing the evidence:
Get a piece of masking tape, about 8-10 cm long. Fold over about 1 cm on each end, to make it easier to manipulate. Press one finger on the sticky side of the tape.
Developing the prints:
Wearing gloves, dip the masking tape into the tray of crystal violet solution and let sit for two to three minutes. Remove the tape, and immediately rinse with tap water. Place the tape (sticky side up) on a paper towel to dry.
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Preparing the evidence:
Wear gloves or use forceps to avoid leaving extraneous fingerprints. Cut a piece of white paper, about 3-4 cm square. Wipe a finger across your forehead, then apply the fingertip to the white paper. Again, do not roll or move the finger while pressing.
Developing the print:
When using iodine, avoid inhaling fumes!
Keep the jar closed as much as possible and do not inhale the iodine fumes. Iodine sublimates (turns from solid to gas) very quickly and produces toxic fumes.
1. Wear gloves to carry out the following steps.
2. Place a few (5 to 8) crystals of iodine in a small jar.
3. Open the jar containing the iodine crystals and quickly put the paper into the jar so that it is not in direct contact with the crystals. Replace the lid and allow the print to absorb the iodine vapor for about 5 to 10 minutes or until the print is visible.
4. Once you can see the developed print, use forceps to remove the paper from the jar. Be sure to quickly replace the lid on the jar to avoid inhaling the fumes. Leave the crystals in the jar.
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