NAME:
Team:
Forensic Science - Fiber Analysis
Background:
Evidence of any kind must be evaluated, and this is true for fibers as well. The value of fiber evidence in a crime investigation
depends on its potential uniqueness. The scientist needs to be able to identify the type of fiber, its color, number of fibers found
at a crime scene, where they were found, the textile the fiber originates from, are there multiple types found, etc. The following
lab is designed to demonstrate some of the procedures used by forensic scientists in their attempt to answer some of these
questions.
Materials:
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Cloth swatches (include 100% samples of: Cotton, wool, rayon, silk, nylon, polyester & blends, 2 inch squares)
Unknown ‘A’ or ‘B’ fabric sample
Thread count card (card with 1” square cut-out with mounted fabric)
Bunsen burner
Crucible Tongs or Forceps
Magnifier or Dissecting Microscope
Toothpicks
Watch glass
6M HCl in dropper bottle
Safety goggles
Apron
Procedure:
Part I - Acid Test
1. For each swatch of cloth, cut a small strip from your sample approximately 1/8-1/4 inch from your swatches.
2. Place it on the watch glass and drop 1-2 drops of 6M HCl. Let sit for 30 seconds.
3. Try to tease the fabric apart and record the results (resistant to acid/non-resistant to acid).
4. Repeat for each type of fabric and record your results in the data table below.
Part II - Fiber Burn Analysis
1. Ignite your Bunsen burner following all proper safety precautions.
2. For each swatch of cloth, hold the cloth over the flame with the crucible tongs so it has a chance to ignite.
3. Remove the cloth from the flame.
*Note whether or not the cloth continues to burn, or does it go out immediately. Does it even burn?
Does it melt or produce an ash?
Does it have an odor (remember the ‘wafting’ technique you were taught in chemistry)?
**DO NOT place your face or nose near the fabric while it is still burning.**
Part III – Thread Count
1. Take the Thread Count Card (card with 1” square cut-out with mounted fabric) and place it under the magnifier or on the
stage of the dissecting microscope.
2.
3.
4.
Count the number of threads going horizontally, in one direction. Record.
Count the number going vertically, in one direction. Record.
Add the two numbers. That will give the thread count. Record.
^Fiber Burn Analysis Key: When fiber is removed from flame:
Step #
Observation
Next Procedure
Conclusion
1
1
It ceases to burn
Fiber continues to burn
Go to Step #2
Go to Step #3
none
none
2
2
Fibers have the odor of burning hair
Fibers do not smell like hair
Go to Step #4
none
polyester
3
3
Fibers produce a small amount of light ash residue
Fibers produce gray fluffy ash
rayon
cotton
4
4
A hard black bead results from burning
A brittle, black residue results
wool
silk
^Bertino and Bertino, Forensic Science: Fundamentals and Investigations, Cengage Publishing, 2012
Textile
100%/Blend
Cotton
Sheen (Luster/
No Luster)
NL
Burn
Odor
Ash
Bead
Y
N
G
N
Acid (Resistant/
Non-Resistant)
R
Jute
NL
N
N
N
N
R
Nylon
L
M
N
N
N
NR
Polyamide/
Spandex Blend
Polyester/
Cotton Blend
Polyester
L
M
N
N
Y
NR
NL
Y
N
N
N
R
L
M
N
N
Y
R
Rayon
L
Y
N
L
N
R
Silk
L
Y
Y
N
N
R
Wool
NL
N
Y
N
Y
R
(light/gray/none)
NAME:
Team:
Data: Fabric Appearance/Test Results:
Color
Sheen (Luster/
Burn
No Luster)
White
L / NL
Y/N/M
Odor
Ash
Bead
Y/N
L/G/N
Y/N
Acid (Resistant/
Non-Resistant)
R / NR
(light/gray/none)
Beige
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
Burlap
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
Brown
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
Grey/Green
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
Purple
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
Floral
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
Pink
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
Plaid
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
Evid. Fiber A
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
L / NL
Y/N/M
Y/N
L/G/N
Y/N
R / NR
Linear Pattern
Evid. Fiber B
Box Pattern
Essay: State which fiber would be best worn in the lab and why?
Best fiber:
Why:
Thread Count Results:
/in2
Identity of Fabric