NAME ______PERIOD ______

FORENSIC SCIENCE

FIBERS, YARNS, and FABRICS IDENTIFICATION LAB

Introduction

In the forensic lab the identification of a fiber or piece of fabric can make or break an investigation. The results of chemical tests vary according to the chemical make up and physical properties. Fabrics can be natural, synthetic (man-made) or a combination of the two.

Natural Fibers

Plant Origin: Cotton, Linen, Jute, Flax

Animal Origin: Wool, Silk, Mohair, Cashmere

Synthetic Fibers

Nylon – made from petroleum

Polyester – made from coal and petroleum

Synthetic/Natural Fibers

Made by taking natural fibers, dissolving them, reconstituting, and forming into fiber.

Rayon

Acetate

Fibers are fine hair-like structure that is divided into two categories, synthetic and regenerated. Fibers are further classified as either filament fibers or staple fibers.

Filament Fibers: smooth and sleek, and of indefinite length, mostly synthetic

Staple Fibers: usually rough, short length, usually natural sources

Tests you will be performing:

1. Visual Observation (appearance) DAY 1

Texture and sheen. Examination of a yarn sample under the microscope will show thread ends all along the length of the yarn and fibers of irregular thickness. Yarns of filament fibers will be shiny, have smooth texture and show fibers parallel to each other.

2. Stain Test – Day 2

A special stain has been produced for the purpose of identifying fibers. The color produced by the stain on a fiber or fabric is based on the chemical and physical properties of the sample.

3. Protein Test – Day 2

Silk and wool are natural animal fibers, which are made from proteins. Proteins contain specific bonds called peptide bonds. When these peptide bonds are exposed to a combination of copper sulfate and sodium hydroxide, a purple color will be observed.

4. Burn Test – DAY 3

Burn testing is generally reliable way of identifying fibers. It is possible to reliably determine whether a fiber is natural or man-made by burning fibers and observing the behavior of the flame and the characteristics of the residue. Three observations MUST be recorded for each sample.

a. Burning Behavior: How the fiber burns

Is it consumed quickly? Does it curl away from the flame?

What color is the flame? Is the burn continuous or does it sputter

or sizzle? Does it continue to burn or glow after the flame is

removed? Is smoke produced? What color is the smoke?

  1. Odor:

Compare the odor to distinctive odors you are familiar with such as burned hair, burned plastic, burned paper.

  1. Residue Characteristics:

Does it form ash or melted beads, or drops?

What color are the beads, ashes or drops?

What is the consistency or the ash, beads or drops?

(fluffy, crumbly, shiny, beaded, powdery, brittle, hard, round)

Materials – Day 1 (per lab group of 4)

1 cm x 1 cm squares of each of the samples (A,B,C,D,E,F)

Hand Lens, Microscope

1. VISUAL OBSERVATION

Six sample squares, Hand Lens

Procedure

  1. Observe each sample through the hand lens.
  2. Record the properties of each fabric sample in the Data Table. Pay special attention to the texture and sheen and the appearance at the edge of the fabric.
  3. Sketch each fabric under low and high magnification.

Materials – Day 2

1 cm x 1 cm squares of each of the samples (A,B,C,D,E,F)

DuPont Staining set-up under hood

2. STAIN TEST

Procedure – ALL lab groups stain the SAME sample at the same time (A first then B then C, then D, then E then F)

FOLD a SHEET OF PLAIN PAER INTO SIX SQUARES LABELED A-F

  1. Add 100 ml tap water to one 150 ml beaker and set aside to rinse the samples.
  2. Warm 30-40 ml of the DuPont fiber ID solution to 70oC in the second beaker on the hot plate. DO NOT BOIL.
  3. Soak fabric sample A in the stain for 1 minute.
  4. Remove the sample from the stain using the forceps and rinse by dipping in the first beaker of tap water. Then repeat rinse in second beaker of tap water.
  5. Remove the rinsed sample and place on prpared sample sheet. Repeat steps a-e for sample B-F.
  6. Use KEY CARD to identify each sample in your data table. Discard all used cloth samples in the wastebasket. Wipe down the lab bench.

Materials – Day 3 (per lab group of 4)

1 cm x 1 cm squares of each of the samples (A,B,C,D,E,F)

SIX-well plate

0.5 M Copper sulfate solution (CuSO4)

3.0 M Sodium hydroxide solution (NaOH)

Forceps

Second hand on wall clock

3. PROTEIN TEST

  1. Place one sample into each well A-F.
  2. Place 5 drops of 0.5 Copper sulfate on the allow it to sit for 5 minutes.
  3. Holding each sample with forceps, dip it into the 3 M sodium hydroxide in a beaker for 10 seconds.
  4. Remove the sample from the sodium hydroxide. Check for color change. A purple color indicates the presence of protein and therefore an animal source.
  5. Observe and record the color of each sample in the Data Table.
  6. Repeat steps a-e for samples B-F.

Materials – Day 3 (per lab group of 4)

Two 1 cm x 1 cm squares of each of the samples (A,B,C,D,E,F)

Forceps

Bunsen Burner

4. Burn Test

Procedure

  1. Prepare a sample sheet as you did on DAY 2. Six squares label A-F with two squares in each box.
  2. When called bring your prepared sample grid, pens and labs to the front of the room for flame test
CONCLUSION

Based on our data, the fiber sample is:

AD

WHY?WHY ?

BE

WHY?WHY?

CF

WHY?WHY?