DECEMBER 5, 2012
EQ: How can synthetic fibers be used to solve
crimes?
WARM-UP:
The following slide will have 9 pictures (A-I).
Identify the animal hair shown and answer the
questions. You may use the pgs in Ch 10
(blue)/11 (orange) of your book.
Can you identify the animal hairs shown?
Think About It …
(1) In which samples are we viewing the cuticle? How do they compare?
(2) In which samples are we viewing the medulla? How do they compare?
(3) What characteristics can be used to identify hair samples?
Types of Animal Hairs - Key
A
Cat
B
Horse
C
Pig
D
Human
G
E
Deer
F
Dog
Rabbit
H
Rat
I
Human
1. All
2. All but two (B & I)
3. Medulla absent or present, shape of medulla, cuticle, diameter
of medulla, etc.
- Root Characteristics: Removal
Pulled
Forcibly removed
Shed
- Tip Characteristics
Burned
Cut
Razored
Split
Fiber Evidence
A fiber is the smallest unit of
a textile material that has a
length many times greater
than its diameter.
Matching unique fibers on the
clothing of a victim to fibers on a
suspect’s clothing can be very helpful
to an investigation.
The discovery of cross transfers and
multiple fiber transfers between the
suspect's clothing and the victim's
clothing dramatically increases the
chances that these two individuals had
physical contact.
Natural Fibers
Many different natural fibers that come from plants and animals are used in the
production of fabric. (Wool, mohair, cotton, cashmere, mink, etc.)
Cotton fibers are the plant fibers most commonly used
in textile materials. Cotton fibers have a ribbon-like
shape with twists at irregular intervals.
The animal fiber most frequently used in the
production of textile materials is wool, and the most
common wool fibers originate from sheep.
http://www.fireflydiapers.com/articles/diaperarticle_naturalfibersabsorb.htm
Synthetic (Manufactured) Fibers
More than half of all fibers used in the production of textile
materials are synthetic or man-made.
Nylon, rayon, spandex, and polyester are all examples of
synthetic fibers.
Cross-section of a
man-made fiber
Fibers under a microscope
Images: http://www.trashforteaching.org/phpstore/product_images/YarnWS.JPG
http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedric3.htm#Fiber%20Evidence
http://www.jivepuppi.com/images/fiber_evidence.jpg
5 Characteristics used to identify Fibers:
1.
2.
3.
4.
5.
Color (comparison microscope)
Diameter (comparison microscope)
Lengthwise striations
Pitting of fibers surface
Cross-sectional shape
Analytical Techniques used in Fiber Examination:
Visible-light micro spectrophotometercompare colors of fivers through spectral patterns
ChromatographySeparating colors in dyes that come from the fibers for comparison
Chemical compositionTest for chemical make-up of fibers to see if they are in the same
class
BirefringenceDouble refraction (two bends), when substance is melted &
crystallized
Infrared LightUse of a microscope and infrared spectrophotometer for infrared
analysis
3 Challenges in Identifying Fiber Evidence:
1.
No analytical
technique to trace a
fiber to a single
garment with certainty
2.
No databases for fibers
origin
3.
Mass distribution of
fibers and changing
fashions
Collection & Preservation of Fiber Evidence:
1. Clothing packaged in paper
bags
2. Carpet, rugs, & bedding folded
carefully
3. Articles shouldn’t be placed on
same surface
4. Loose fibers removed and
placed on paper, folded and
labeled
HAIR & FIBERS DRAWINGS:
Draw the following fibers and include the following:
1. Specimen name (Dog, cat, etc.)
2. Magnification (100x, 400x, etc.)
3. Contain a Medulla
4. Is medulla continuous, fragmented, or
interrupted?
HAIR:
Human
Dog
Deer
Rabbit
Cat
Mouse
Draw the following NATURAL & SYNTHETIC fibers as seen
under a microscope and include the following:
1. Specimen
2. Magnification
3. One characteristic
4. Uses (at least two)
Cotton
Wool
Mohair
Rayon
Polyester
Spandex
Can you identify the types of fibers shown?
Think About It …
(1) Which samples are natural fibers?
(2) Which samples are synthetic fibers?
(3) What characteristics can be used to identify fiber samples?
Answer
Keys
http://micro.magnet.fsu.edu/primer/techniques/polarized/gallery/images/humansmall.jpg
Types of Fibers - Key
Acrylic Yarn
Cotton Yarn
Nylon Rope
Polyester Yarn
Rayon Rope
Wool Yarn