Forensics Fiber Analysis, Summaries of Forensics

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Fiber Analysis

Fibers

• Individual or Class Evidence?
  • Class
  • Even if fibers from two separate places can be matched via comparison, that does not mean they derive from the same source
• Direct Transfer: from victim to suspect or from suspect to

victim

• Ex. from suspect’s sweater to victim
• Secondary Transfer: when fibers are transferred from an

original source to one person and then to a second person.

• Ex. Carpet (fibers) à Victim Victim à Suspect
• Ex. Pet (fur) à Suspect Suspect à Victim

What Questions Do Forensic Scientists Ask about Fibers?

1. What is its composition?
2. What is its color?
3. Is it common or rare?
4. How many fibers were found?
5. Where were the fibers found?
6. What type of textile did the fiber originate from? (carpet, clothing, upholstery, etc.)
7. How many different types of fibers were transferred? The more sources of fibers, the longer or more violent the contact.
8. What type of crime was committed and does the amount of fiber transferred match with what would be expected given the type and duration of contact?
9. How much time has passed between the crime and the discovery of fiber? Come up with at least 5 Questions!

How is Fiber Collected?

• Vacuums

• Sticky Tape

• Forceps

• With very accurate

record of where

fibers were found.

Textiles

• Textiles: clothing, carpet, upholstery.

• Made by weaving together yarns.
• Yarns: made up of fibers that have been spun together.

• 2 Types of Fibers:

1. Natural: come from animals, plants, and minerals
2. Synthetic (man-made): regenerated fibers & polymers

• 50% of fabrics made today are synthetic (man-made) Check your neighbor’s labels!

Natural Fibers

1) Animal Fibers

– Made of proteins.

– Used in clothing, carpets, curtains, bedding.

– Obtained from hair, webbing, or fur:

• Hair – wool (sheep), cashmere and mohair (goats), angora

(rabbits)

• Usually loosely spun, making textiles that shed easily.
• Webbing – Silk (caterpillar cocoons)
• Triangular structure gives silk its shiny appearance (works like a prism).
• Silk fibers are very long, tend not to shed easily
• Fur – not considered a textile , used for coats and gloves

Natural Fibers Types of Plant Fibers

1) Seed fibers

• Cotton (found in seedpod)

2) Fruit fibers

• Coir – coarse fiber obtained from the covering of coconuts. Stronger than flax or cotton.

3) Stem Fibers – not individual fibers, found in bundles

• Flax – highly crystalline, dense strong fibers that resist rot and damage, used to make linen
• Jute – coarse; used to make rope, mats, handbags
• Hemp – similar to flax, used in Asia for clothing

4) Leaf fibers

• Manila – extracted from the leaves of abaca (relative of banana tree)
• Sisal – desert plant; used for rope, netting, green garden twine, twine on hay bales; quick deterioration

Natural Fibers

3) Mineral Fibers

– neither protein, nor cellulose

– Fiberglass – short, weak, brittle glass fibers, used

as insulation, easily sticks to skin (causing rash)

– Asbestos – very durable; used in pipe coverings,

ceiling tiles, fire-resistant work clothes, insulation

Synthetic Fibers

2) Synthetic Polymer Fibers

• Originate from petroleum products (non-cellulose based).
• Many can be easily dyed.
• Examples:
  • Polyester – added to natural fibers to increase strength
  • Nylon – similar to polyester; but easily broken down by light and concentrated acid (polyester is resistant to these); first used as artificial silk in pantyhose
  • Acrylic – artificial wool; clothing tends to pill easily; inexpensive
  • Olefins – high performance clothing (thermal socks) and carpet; quick drying; resistant to wear

Synthetic vs. Natural

• Synthetic fibers:

• Are stronger than natural fibers.
• Are not damaged by microorganisms.
• Are often cheaper than natural fibers.
• Can deteriorate in bright sunlight & melt at lower temperatures.
• Have very regular diameters under magnification. Polyester Cotton

Textiles

• Yarns are woven into textiles or fabrics.

• Weaving originated with basket-making.

• Stone Age man used flax fibers to weave linen.
• Bronze Age – wool fabrics
• Oldest Loom – Egyptian tomb 4400 B.C.
• Warp (lengthwise) and weft (over-under)

• Thread Count – number of threads

packed together

• Ex. Bed sheets
• Highest Cost Textiles - all natural fibers and high thread count (ex. 500 threads per inch)

Weave Patterns - pattern of the warp and weft

(the lengthwise and crosswise threads)

1) Tabby (plain)

• Over 1, under 1 (1/1 weave).
• Simplest, most common.

(cont’d)

3) Satin

• 3/1, 4/1, 5/1, 6/1 or more.
• Smooth and silky on one side, dull on the other.

(con’t)

• 4. Basket Weave

– Multiple horizontal and multiple vertical strands

• 5. Knit

– Courses and wales