Fingerprinting

Age

Middle School, High School

Format

Hands-on

Matierials

Inkpad

Charcoal

Magnifying lens

Laminated evidence

Fingerprinting worksheet

Baby wipes

Safety Precautions

Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience.

Preparation

Most materials will be kept in the boxes marked 'Forensics' along with a printed copy of these instructions.

Demonstration

I. Introduction

Introduce Science Theatre and this demo. If using this demo with the crime scene, explain the story behind the crime. A copy of this is found in the Forensic boxes.

II. Fingerprint Basics

a) Patterns

First explain the different types and patterns of fingerprints.

Loops:

• Present in 60-70% of the population.
• Radial loops begin and end in the direction of the thumb and are very uncommon. They are usually found on index fingers.
• Ulnar loops begin and end in the direction of the pinky/little finger.

Whorls:

• Present in 25-35% of the population.
• Plain whorls consist of one or more ridges which make a complete circuit with two deltas. There is at least one re-curving ridge.
• Central Pocket whorls consist of at least one re-curving ridge or an obstruction to the line of flow and have two deltas. The pattern makes a complete circuit which may be spiral, oval, circular, or a combination of the three.
• Double Loop whorls consist of two separate loop patterns, each having their own distinct shoulders. There are two deltas and one or more ridges which make a complete circuit with at least one re-curving ridge.
• Accidental whorls consist of a combination of any whorl pattern, excluding the Plain whorl pattern. There are at least two deltas. It may conform to multiple or none of the other whorl requirements.

Arches:

• Present in 5% of the population.
• Plain arches have an even flow of ridges from one side to the other.
• Radial arches slope in the direction of the thumb.
• Ulnar arches slope in the direction of the pinky/little finger.
• Tented arches have an angle, similar to a loop, and an uneven flow.

b) Types

Visible prints:

• Visible without any scientific assistance.
• Impressions in or on a visible surface (i.e. dust or an impression).

Latent prints:

• Cannot be seen without scientific assistance.
• Created from the oils in our fingers and must be processed in order to be seen.

c) Basic information:

• Ridges are what create our fingerprints. They form during our fetal development.
• The purpose of ridges is to create friction and allow us to pick things up. If a person did not have ridges, they would drop everything they tried to hold.
• Each ridge pattern contains rows of pores. They allow sweat and oils to exit through the ridges. The transfer of oils is the cause of fingerprints.
• No two people have the same fingerprints. Even identical twins do not have the same fingerprint, but can have similar patterns.
• Some criminals try to "erase" their fingerprints. This can include using acid to burn off their finger pads. However, this is ultimately unsuccessful and can actually aid the police in their investigation (e.g. scars, unique markings, damaged finger pads). Damaged prints can reform and grow back in the same original pattern.
• Your fingerprints never naturally change. he fingerprints you are born with are the same fingerprints you will have for your entire life.
• To fingerprint animals, some scientists use the animal's nose as its markings are just as unique as fingerprints.

III. How to Roll a Fingerprint

Demonstrate how to roll a fingerprint onto the worksheet.

1. Press an individual finger in the ink, covering the pad completely.
2. Place the finger onto the worksheet. Begin with the side closest to the thumb on the paper, then roll in the direction of the pinky/little finger. Gently lift the whole finger from the paper, revealing a complete print.
3. Place all five fingers on the worksheet at once. Simply press and lift all four fingers at the same time, then the thumb individually.

Explain the difference between the rolled fingerprints and the pressed fingerprints.

• The pressed fingerprints allow us to view and measure the spacing and length differences between each finger.

Allow the participants to take their own fingerprints.

IV. Extraction Methods

Explain how fingerprints are extracted from a crime scene.

Hinge lifters:

1. The plastic sheet of the lifter is placed over the area of the fingerprints.
2. A roller is moved over the sheet, removing any air bubbles.
3. The sheet is lifted and pressed onto the glass or plastic background.
4. The roller is again moved over the lifter.

Rubber lifters:

1. A plastic cover is first removed from the rubber adhesive in one steady motion. Any pauses will cause the entire lifter to be unusable.
2. The rubber adhesive is pressed onto the area of the fingerprint.
3. The adhesive is gently lifted in one steady motion. Any pauses will cause the entire lifter to be unusable.
4. The plastic cover is replaced over the adhesive.

Cellophane tape lifters:

• These lifters are useful for surfaces that are uneven or not flat.

1. A small edge of the tape is folded over itself to create a tab for handling.
2. The tape is placed over the area of the print and rubbed, removing any air bubbles.
3. The tape is gently and evenly removed from the surface.
4. It is then applied to a card or paper and the excess tape is cut away.

V. Analysis

Allow the participants to compare the results of their fingerprints with the fingerprints of the suspects.

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To use this demo as a stand-alone from the crime scene, simply exclude all information pertaining o the suspects.