Bob Flashcards
What are the 3 types of Fibre exchange?
Between:
- two individuals
- an individual and object
- two objects
If fibre transfer occurs, and can be detected depends on… (3 Factors)
The fibres persistence
The type of fibre and fabric
The nature and duration of contact
What is shedability
The potential for a fabric to transfer fibres
What is the order of shedability?
Most Wool Acrylic Cotton Viscose Polyester Nylon Least
A way to get an idea of the shedability of a fabric?
A simple tape lift
Direct transfer —
fibre transferred from fabric directly onto victim or suspect
Indirect Transfer -
fibre already transferred onto clothing of suspect or victim transfer onto the other party
Secondary Transfer
is one caused by contact between two items in which material on one item presents itself as a trace contact material, is transferred to the second recipient item
Tertiary Transfer
is an indirect transfer involving the donor item as an intermediary surface
What are the Four types of comparison and Identification
Mechanical Fit
Microscopic comparison
Chemical Composition
Colour Comparison
What is Mechanical Fit?
where fabric is torn and placed back together to show that it once was whole, conclusive evidence
What happens during microscopic comparison?
compound microscope - comparison of hair/fibres
Polarized light microscope - optical properties/morphology of materials
comparison microscope - side-by-side viewing of fibres
Give 3 Influencing factors of shedding
Age of Fabric
Damage
Construction
How does the age of a fabric influence shedding?
If a fabric is older/worn it is more likely to have been damaged which increases shedding.
Newer Fabrics may have loose fibres adhering to the surface
How does damage affect fabric shedding
If during the contact, there is increase physical contact and the fabric is damaged the fabric will shed more
How does the construction of a fabric affect shedding
Tightly woven or knitted fabrics are less likely to shed, shedding is also dependant on the type of fabric
Which is likely to shed more, a filament yarn fabric or a woven one
Woven yarn
Why would you use one-to-one taping?
Surface area taping of exposed areas of body and clothing
positions of fibre tapings are catalogued and can be associated later for a distribution map
What are the limitations of fibre taping?
Drawbacks (i) unsuitable on heavily contaminated items where large amounts of particulate debris, (ii) use difficult on angular or irregular surfaces, (iii) not easily used on large surface areas
how are synthetic fibres formed?
by extruding a fibre- forming
substance, called spinning dope, through a hole or holes, n a shower-head-like device called a spinneret
What can the cross-section of a synthetic fibre show?
can show the intended use of the fabric
If a synthetic fibre has a trilobal or lobal cross section, what is its intended use?
Carpet - to hide dirt and create a visual texture to the carpet
Name 3 other possible shapes, other than tri-lobal for the cross section of a fibre
dog-bone
round
irregular
Give 3 methods of fibre analysis
TLC
infra-red
colour analysis
What is pleochromism
The property causes substance to show different absorption colours when it is exposed to polarised light coming from different directions.
what is beneficial about a pleochromism of fibres?
it is easy to compare fibres suggesting or disproving connection
what does the micro-spectrophotometer do?
Allows for an objective measurement of the colour
of small, millimetre, or microscopic samples and are
more precise, quantitative or objective compared to the more subjective results of visual macroscopically colour
comparisons.
What is tlc used for in fibre analysis?
separates dyes from fibres and hairs and is highly discriminatory, but is a destructive test
What is infra-red used for in Fibre analysis?
Infrared light has energy to stretch, bend and
vibrates bonds in materials. The energy absorbed
is measured and produces a fingerprint of the
fibre. IR databases are in existence.
What is a possible disadvantage of using adhesive tape to remove fibres?
Overloading the tape with background fibres will make it difficult to search and reduce the adhesiveness of tape
What are the steps of fibre recovery?
Using transparent adhesive tape
Holding adhesive side down
Systematically dabbing the surface
Tape is then stuck down onto acetate sheet
Placed in greaseproof envelope
Alternatively a roller may be used to roll across the garment (replacing tape as required
