1. Collection, Testing and Determination of Uniqueness
Deedrick, D. W. Hairs, fibers, crime, and evidence, Forensic Science Communications [Online]. (July 2000). Available:
Fibers
Collection, Testing and Determination of Uniqueness
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Types of Fiber
Image of cotton fibers.
Natural-
Any fiber that comes from plant or animal sources, examples?
Cotton, wool, silk, linen, angora, cashmere, and hemp are some examples of natural fibers. All furs are also natural fibers.
Deedrick, D. W. Hairs, fibers, crime, and evidence, Forensic Science Communications [Online]. (July 2000). Available:
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Types of Fibers Cont’d
Synthetic-
Any fiber that is made in a laboratory, examples?
Image of nylon.
Examples of synthetic or manmade fibers are nylon, acetate, rayon, polyester (Underarmor), polypropylene (bicycling clothing), kevlar, lycra, and spandex. Orlon & Dacron are types of carpet fibers.
Deedrick, D. W. Hairs, fibers, crime, and evidence, Forensic Science Communications [Online]. (July 2000). Available:
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Testing
Fibers are generally identified by type of cloth and color by
Physical Properties
Burn test
Melting test
Solubility
Optical properties
Dye identification
What are some physical properties? Color, shape, texture, mass, volume, density, etc. Yhese are the physica; properties used to identify fibers
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5. Burning and Melting Tests
Place the fiber in a flame and record the results.
Heat the fiber on a hotplate and record the results.
Changes in physical properties: color, smoke, smell, etc.
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Solubility Test
What is it soluble in?
Strong base
Strong acid
other
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Optical Properties
These are the tests that are currently used to identify fibers.
Behavior in
visible,
IR,
UV and
polarized light
Image from
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Identification of Dye
Thin Layer Chromatography
Separates molecules based on the affinity to the surface they are placed on versus their solubility in the solvent they are being dissolved in
Low solubility in solvent and high adhesion to the surface--- does not go very far
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Image from
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Comparison?
How is the fiber from a scene compared to fiber from a known source?
All the characteristics found on the known fiber and the questioned fiber must be identical.
What does it mean to say they are similar fibers?
Class
Individual
Fiber has on class characteristics. In our world today, thousands of yards of different fibers are produced and sold each year. A forensic scientist can only say that two fibers are consistent with each other.
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Characteristics
Individual
Class
High probability of linkage with only one individual.
One of a kind? unusually made fiber made in very small amount with unusual dye
Consistent with a group
It would take very unusual circumstances to be able to say that fibers had individual characteristics; circumstances such as the fiber was special ordered and only made in a very small amount with unusual make-up and dye.
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Fiber Collection
Cellophane tape into Petri dish or
Vacuuming
Choose container that will prevent loss
Label and
Seal
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Comparison of Fibers
Fibers from victim’s fingernail to known sample from suspect’s sweater.
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Control Samples
From victim & suspects’ homes and vehicles
Uncontaminated
Large enough to do testing needed
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