Hair and Fibers Flashcards
fiber definition
the smallest unit of a textile material that has a length many times greater than its diameter
how do fibers occur?
- naturally as plant and animal fibers
- synthetic, man-made
hairs and fibers - evidence types
- biological &/or physical
- indirect
- trace evidence
- class
4 categories of fibers
- animal fiber
- vegetable fiber
- mineral fiber
- man made fiber
animal fiber
wool is most common, but only 1% of textile fibers
vegetable fiber
- 24% of all textile fibers
- cotton is most common
mineral fiber
- rare
- only asbestos
man made (synthetic) fibers
75% of all textile fibers
characteristics of synthetic/man made fibers
- uniform
- variety of shapes
- absence of features
characteristics of animal & vegetable fibers
- irregular only
- circular to oblong
- visible features (cuticle & medulla)
what do fiber analysts compare?
- shape
- dye content
- size
- chemical composition
- microscopic appearences
fiber association
- fibers from two separate places can be associated via comparison, that does not mean they derive from the same source
- there is no fiber database that provides a probability of origin
Fiber Population Studies
relative frequencies of fiber type/color (generic) on particular surfaces
Color Block Studies
ability of a specific protocol to discriminate between similar fibers (type/color)
Target Fiber Studies
probability of finding significant numbers of a specific fiber type by random chance
direct transfer of fibers
fibers may be transferred from a victim to a suspect
example of direct transfer of fibers
fibers from victims sweater found on suspect
secondary transfer of fibers
fibers are picked up by victim and then transferred to suspect
example of secondary transfer of fibers
victim picks up fibers from his/her couch earlier in day & then transfers to the suspect later
how is primary vs secondary transfer determined?
can be determined if the order of events is known
what kind of timing is essential for fiber collection?
early collection
why is it essential that fibers are collected early?
within 24 hours an estimated 95% of all fibers may have fallen off a victim or been lost from a crime scene
which fibers at the crime scene are investigated?
only fibers not expected to be found at a crime scene are investigated
textile shedding
the most common form of fiber transfer to be encountered is the shedding from a textile
textile (fabric)
a flexible, flat material made by interlacing yarns
examples of textiles
- clothing
- carpets
- upholstery
which is the smallest: fiber, yarn, textile
fiber
which is the biggest: fiber, yarn, textile
textile
5 major types of weave patterns
- plain
- basket
- satin
- twill
- leno
what determines the weave pattern?
warp and weft
warp
length wise fiber
weft
crosswise fiber
plain weave pattern
- alternating warp & weft pattern
- single fibers
basket weave pattern
- alternating warp & weft pattern
- double fibers
satin weave pattern
weft goes over 3 or more warps
leno weave pattern
adjacent weft threads cross over each other
twill weave pattern
- weft goes over two then under two warps
- warp goes over two then under two wefts
thread count
threads per inch
high thread count =
higher price
what kind of fiber analyzing techniques are prioritized?
non-destructive techniques
dyes can be analyzed with Thin Layer Chromatography (TLC)
dye components are separated by their differential migration caused by a mobile phase flowing through a porous, absorptive medium
what are the variations of hair?
- color
- length
- diameter
- body distribution
how are hair variations influenced?
influenced by ancestral affinity and age
3 main parts of hair
- cuticle
- cortex
- medulla
cuticle
outside transparent covering
cortex
- 2nd layer made of keratin & embedded with melanin
- contains air sacs called cortical fusi
- gives hair color, form, and shape
medulla
- innermost layer running down the center of the cortex
- gives hair its flexibility & offers insulation
advantages to hair toxicology
- easy to collect and store
- externally available
- can provide info on the individuals history of drug use or evidence of poisoning
animal cuticle types
- coronal
- spinous
human cuticle type
imbricate
medulla types
- fragmentary
- interrupted
- continuous
- stacked
- absent
human medulla types
- fragmentary
- interrupted
- continuous
animal medulla types
- continuous
- stacked
medullary index
width of medulla / width of cortex
typical human medullary index
0.33 or less
typical animal medullary index
0.50 or more
collecting hairs
collect 30-50 hairs from each body region
Postmortem Root Band (PMRB)
proteomic analysis of decedent scalp hair segments exhibiting a postmortem hair root band
