Materials Included In Kit

Additional Materials Required

Safety Precautions

The BioFoam contains ≤ 1% formaldehyde. It causes skin and serious eye irritation. It may cause respiratory irritation and cancer. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. List each chemical and/or product and the proper disposal method. All materials can be disposed of according to Flinn Suggested Disposal Method #26a in the regular trash or saved for future use.

Lab Hints

• This lab was tested mixing calcium sulfate hemihydrate with tap water. However, depending on your water quality, it may be necessary to use distilled or deionized water.
• If you wish to perform this activity as a class with a forensics angle Flinn Scientific offers Flinn Forensic Files—Footwear Evidence Classroom Set, AP7752.

Teacher Tips

• Enhance the story by allowing students to perform the other lab kits in the Flinn Forensic Files Series:
  • FB2094, Flinn Forensic Files—Fingerprint Exploration
  • AP7745, Flinn Forensic Files—Ink Inspection
  • FB2096, Flinn Forensic Files—Finding Evidence in Fibers
  • AP7050, Flinn Forensic Files­—Ballistics

Answers to Prelab Questions

1. Why are footprints present at almost every crime scene?

   A person committing a crime must, in some way or another, enter and exit the crime scene. This is most often done on foot, even if only for a short distance, making footwear prints available at almost any crime scene.

2. What challenges do you envision detectives experiencing when attempting to take footwear impressions at actual crime scenes?

   The medium that the footwear print is in can present additional challenges. For example, snow is not as easy to cast as mud. Also, weather conditions can alter the prints. If it has rained heavily since the print was made it may not be usable at all.

Sample Data

Answers to Questions

1. Record the length and width of the footwear print in the Observations Table.

   Student answers will vary.

2. Record any distinguishing characteristics from the shoe impression, such as unique tread patterns, brand names, etc.

   Student answers will vary.

3. Sometimes more than one suspect is possible based on the footwear analysis, what other tests could be done to determine the guilty party?

   Investigators could also search the crime scene for fingerprints, hair and fiber analysis and DNA to further determine the guilty party.

Introduction

Tracks left by footwear are a valuable piece of evidence at crime scenes that is often overlooked. Learn the different ways that tracks from shoes can be used to develop possible suspects in a criminal case.

Concepts

• Forensics
• Footprint impressions/casting

Background

Footwear impressions are often used to place a suspect at a crime scene. It makes sense that a criminal must enter and exit the crime scene on foot at least for a short distance, making the footwear impression a common denominator in most crime scenes. Criminals have realized it is important to conceal their fingerprints with gloves or their faces with masks. In fact, in the wintertime you might not think anything of a person wearing either of those accessories. However, most people don’t wear shoe covers in their daily lives and doing so would make a person stand out.

Footwear evidence is obtained by prints or impressions. Just like fingerprints, footwear prints can be visible or latent. Visible prints are found when the footwear is contaminated by a foreign object such as blood or wet paint. The person then steps on a clean surface leaving a visible print. Latent prints are commonly overlooked as they are not visible unless they are dusted with powder just like fingerprints. Footwear evidence can also be obtained by taking impressions. Impressions are taken when the footprint is evident on a softer surface such as wet sand, mud or snow. First, the medium is treated with a hardening spray followed by casting similar to that used to take dental impressions. Once the casting material has hardened, the 3-D model can be compared to suspects’ footwear as well as saved with other evidence for future reference.

Experiment Overview

In this experiment, the casting of one group member’s shoe will be made using BioFoam and calcium sulfate.

Materials

Prelab Questions

1. Why are footprints present at almost every crime scene?
2. What challenges do you envision detectives experiencing when attempting to take footwear impressions at actual crime scenes?

Safety Precautions

The BioFoam^® contains ≤ 1% formaldehyde. It causes skin and serious eye irritation. It may cause respiratory irritation and cancer. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Making the Impression

1. Obtain a box of footwear foam and open it carefully. Note: Touching the foam with your fingers, even lightly, will leave an impression.
2. Select a group member to make a footwear impression.
3. Step gently onto the foam, depressing your shoe about half-way through the foam. Do not place too much weight on the impression foam.
4. Carefully remove your shoe from the foam. Another group member may need to hold the box down so the impression is not damaged by wiggling your foot to remove it.
5. Very lightly sprinkle talc powder over the impression to serve as a fixative. Tap the sides of the box over a garbage can so that that talc is evenly distributed over the impression.

6. Measure 425 g of calcium sulfate in a 1-gallon resealable bag.
7. Measure 215 mL of distilled water and add it to the plastic bag containing the calcium sulfate.
8. Seal the bag making sure it is completely closed.
9. Shake the bag vigorously for 30 seconds.
10. Gently knead the contents of the bag for 1–2 minutes. Verify that the contents of the bag are not lumpy and are roughly the consistency of pancake batter. If not, add 10 mL more water at a time until desired consistency is achieved.
11. Open the top corner of the bag and gently pour it at an angle into the foam casting. Do not pour directly on the casting where the flow of the material will change the cast.
12. Allow the casting to harden for 30 minutes or until hard to the touch.
13. Remove the casting and foam from the box.
14. Gently peel away the layers of foam from the casting. Note: As the foam is removed, check that the casting has properly solidified before vigorously removing excess foam.
15. Once the impression has completely hardened, clean off the excess foam by brushing the impression with a beaker brush to remove foam from the smaller grooves of the impression.

Student Worksheet PDF

12491_Student1.pdf