Fiber Basics
This principle states that when two objects come into contact there is an exchange of material; name it.
Locard’s Exchange Principle.
Name two natural fibers and two synthetic fibers.
Natural: cotton and wool. Synthetic: polyester and nylon.
Name one method to collect loose fibers from a small surface.
Tape lifting using adhesive tape.
Which microscopy method uses low magnification (10–40x) to view fiber surface details and sort samples?
Stereomicroscopy (stereo microscope).
What lab technique separates dye components on a plate to compare dyes visually?
Thin-layer chromatography (TLC).
Give two reasons why fiber evidence can be important in a criminal investigation.
Link suspects to crime scenes; corroborate witness statements; reconstruct events.
What is a semi-synthetic fiber? Give one example.
A fiber made from natural material that has been chemically processed. Example: rayon.
Why should fibers be packaged separately after collection?
To prevent cross-contamination and preserve the association between fibers and their source.
What is the magnification range for compound light microscopy used on fibers?
About 40x–400x.
Name the chromatography method more precise than TLC for dye analysis.
High-performance liquid chromatography (HPLC).
Explain one major limitation of fiber evidence that investigators must consider.
Most fiber evidence is class evidence, not unique. Matches increase probability but rarely prove identity alone.
Explain how cross-sectional shape and diameter help differentiate fiber types.
Cross-section and diameter affect light interaction and strength, helping distinguish fibers under a microscope.
Outline the four steps you would document before and during fiber collection at a crime scene.
Photograph the location, note position and context, collect using the chosen method, and label and package separately.
Which spectroscopy techniques uses UV light to identify chemical composition of fibers.
UV-Vis microspectrophotometry.
List the primary difference between primary and secondary fiber transfer.
Primary transfer occurs directly from the source. Secondary transfer occurs through an intermediate object or person.
Describe three physical characteristics you would note during a visual examination of a fiber.
Color, length, diameter, texture, crimp/waviness, or luster.
Describe the internal structural difference between crystalline and amorphous regions in fibers and why that matters.
Crystalline regions are ordered and strengthen fibers; amorphous regions are disordered and provide flexibility. Both affect optical and mechanical properties.
Compare tape lifting and vacuuming: give one advantage of each for fiber recovery.
Tape lifting allows precise recovery from small areas. Vacuuming covers larger areas and recesses.
Which spectroscopy techniques uses Infrared light to identify chemical composition of fibers.
Fourier-transform infrared spectroscopy or FTIR
Explain how dye class (e.g., acid, disperse, direct) can help narrow down fiber origin.
Different dyes are suited to different fibers. For example, acid dyes are commonly used for wool and silk, while disperse dyes are commonly used for polyester.
Define "persistence" of fiber evidence and list three factors that affect persistence.
Persistence is how long fibers remain on a surface. Factors include activity level, surface texture, environmental conditions, and time since transfer.
Identify two surface features visible on fibers and explain how they aid forensic comparison.
Scales, such as those on wool, and striations can help identify fiber origin and manufacturing processes.
Explain the concept of chain of custody and why it is essential for fiber evidence admissibility.
Chain of custody is the documented record of evidence transfers that helps maintain evidence integrity and admissibility.
A victim has many fibers on a sleeve and a few on a shirt cuff. Explain what this pattern might suggest about the interaction and why context matters.
The pattern might suggest more intense contact on the sleeve area, such as during a struggle. However, investigators must consider alternative explanations, including secondary transfer.