Fiber and Soil Analysis

Question 1

what is a textile?

Answer 1

• flexible material consisting of network of natural or artificial fibers (yarn or thread)
• formed by weaving, knitting, crocheting, knotting, or felting

Question 2

what is a fiber?

Answer 2

threadlike strand used for spinning yarn (smallest unit)

Question 3

what is yarn?

Answer 3

continuous length of interlocked fibers used for manufacturing textiles

Question 4

what is a thread?

Answer 4

multiple yarns plied together producing a long, thin strand used in sewing or weaving

Question 5

what are the warp and weft of weave patterns?

Answer 5

• warp = threads strung over loom, holding tension while weaving
• weft = threads woven between warp threads, creating pattern and structure
• weave patterns can create very different qualities of fabric (plain, basket, satin, twill, etc.)

Question 6

what do fiber-plastic fusions indicate?

Answer 6

forceful contact in vehicle accidents and other impacts

Question 7

what does reconstruction indicate?

Answer 7

contact with limited suspects

Question 8

what is active transfer?

Answer 8

copious amounts of fibers link transfer to specific, uncommon event (EX: damaged textile from tearing fabric to bind victim)

Question 9

what is the difference between dyes and pigments?

Answer 9

• dyes = soluble; permeate fiber
• pigments = insoluble; physically and chemically unaffected

Question 10

what can fiber evidence reveal?

Answer 10

• identification and classification (natural vs manmade, generic type and sub-type)
• manufacturing info (source textile type, manufacturer)
• physical damage and surface characteristics (circumstances, fracture match)
• comparison (color, diameter, inclusions, cross-section)

Question 11

what are the categories for natural and synthetic fibers?

Answer 11

• natural (animal, vegetable, mineral)
• synthetic (regenerated, totally synthetic)

Question 12

what are most animal fibers derived from?

Answer 12

proteins - hair (besides silk)

Question 13

what are notable natural fibers?

Answer 13

• cotton (seed fiber)
• hemp (bast fibers/plant stems)
• asbestos (mineral)

Question 14

what are regenerated fibers?

Answer 14

• type of synthetic fiber
• natural polymers which are regenerated to form longer chains (most made from cellulose)

Question 15

how is cellulose regenerated?

Answer 15

acetylated with acetic anhydride (remove OH to allow cellulose polymers to float free)

Question 16

what can synthetic fibers be made into?

Answer 16

plastics (Nylon 6,6)

Question 17

what is the only synthetic fiber that is less dense than water?

Answer 17

olefins (polyethylene)

Question 18

what are some of the analytical strategies for fibers?

Answer 18

• morphology (for natural fibers and rayon)
• color comparison (dyed fibers)
• damage (FTIR tear, cut, melt)
• surface debris (microspectrophotometry)
• solubility testing
• size
• cross-section (round, trilobal, ribbon, bean)
• delusterants (small particles to make less shiny)
• indication of processing (crimp, weave)
• birefringence
• sign of elongation

Question 19

what is important when doing color comparison of fibers?

Answer 19

• sufficient number and variety of known samples
• should be conducted under several different lighting conditions

Question 20

what is metamerism?

Answer 20

when color perception is affected by background in which it appears

Question 21

are dyes unique between manufacturers?

Answer 21

no

Question 22

how are synthetic fibers manufactured?

Answer 22

• spinnerets have multiple holes so that numerous fibers can be produced simultaneously to form continuous filaments of semi-solid polymer
• at some point after spinning, drawing occurs (filaments are stretched, pulling the molecular chains together and orienting them along fiber axis - strengthens the fiber)

Question 23

what is microspectrophotometry (MSP) used for?

Answer 23

differentiating colors from dyes, inks, and other substances

Question 24

what is polarized light microscopy (PLM) used for?

Answer 24

determining sign of elongation and estimate birefringence

Question 25

what is Fourier transform infrared (FTIR) spectrophotometry used for?

Answer 25

confirmatory identification

Question 26

what is soil?

Answer 26

- layer(s) of generally loose mineral and/or organic material that are affected by physical, chemical, and/or biological processes at or near the planetary surface - usually holds liquids, gases, biota, and supports plants

Question 27

what is the difference between soil and dirt?

Answer 27

soil can support life while dirt has lost the ability to support life (EX: tracked in dirt inside)

Question 28

what is the organic component of soil made of? what is soil that is only comprised of organic compounds?

Answer 28

- humus (decayed plant and animal remains) - peat

Question 29

what is the inorganic component of soil made of? what is soil that is only comprised of inorganic compounds?

Answer 29

- minerals - sand

Question 30

why is soil significant in investigations?

Answer 30

- violent crimes often occur/end up on ground - criminals frequently bury bodies and other evidence - crimes involving a vehicle (especially if used to dispose of evidence in a remote location) often involve driving in soil - soil is everywhere and varies in composition within meters not miles - soil evidence is commonly transferred to shoes, clothing, carpets, shovels, tools, tires, wheel wells, floormats, and vehicle trunks - soil transfers often go unnoticed - soil varies horizontally and vertically - most transfers only involve topsoil but can interact with other layers

Question 31

how is soil used as class evidence?

Answer 31

- not sufficient to individualize to single location - can refute false alibi - can profile unknown samples to provide leads (roadside, riverbank, industrial, etc.)

Question 32

how is soil evidence analyzed and compared?

Answer 32

- color - texture (particle and density distribution) - stratification (layers) - percent organic content - pH - mineral identification (PLM or X-Ray Diffraction)

Question 33

what are the three components of soil color?

Answer 33

- hue = dominant wavelength (blue, green, red, etc.) - value = brightness - chroma = saturation

Question 34

what are the size comparisons of soil texture components?

Answer 34

sand (largest) then silt then clay (smallest)

Question 35

how is particle size analysis of soil done?

Answer 35

- after drying, soil is weighed and gently shaken through series of sieves (each with finer mesh) - contents of each sieve are weighed

Question 36

how is density distribution of soil done?

Answer 36

- density gradient column with two immiscible liquids of different densities - high density layered on top of low density to form gradient - soil added to column; sink until reach neutral buoyancy

Question 37

how is percent organic of soil determined?

Answer 37

sample dried, ground up, weighed, and pyrolyzed to be weighed again

Question 38

natural soil pH reflects the combined effects of what?

Answer 38

- climate - organic and mineral content - elevation and drainage - time of year

Question 39

what has lower pH and why? silt, sand, clay

Answer 39

sand because water is able to pass through it more quickly

Question 40

what elements have the greatest effect on pH?

Answer 40

Calcium, Magnesium, and Potassium (raise pH)

Question 41

are areas of forest or grass more acidic?

Answer 41

forest