Fibre and textile examinations compare morphology, optical behaviour, polymer or dye characteristics and fabric structure. Shared findings can support association without identifying one garment or establishing the time and route of transfer.
Keep questioned and known materials separate. Select a sequence that preserves limited material and records controls, within-source variation and examination limits.
By the end of this topic you will be able to:
- Distinguish fibre families and textile structures.
- Explain microscopy, polymer and dye comparison.
- Evaluate source correspondence, transfer and persistence separately.
- Birefringence
- Difference between relevant refractive indices under defined conditions; not a simple natural-versus-synthetic test.
- Cross-section shape
- A potentially informative shape that can vary with fibre manufacture and preparation.
- Microspectrophotometry (MSP)
- Microscale spectral measurement of colour response under controlled conditions.
- Pyrolysis-GC-MS
- A destructive polymer-analysis method requiring suitable reference and method interpretation.
- Tape lift
- Adhesive recovery selected for the substrate and target, with contamination controls.
- Yarn twist
- Twist direction and frequency in a yarn, considered with other textile features.
Fibre Families: Natural, Regenerated, Synthetic
Distinguish natural, regenerated and other manufactured fibres using appropriate evidence. Rayon is regenerated cellulose and does not simply melt; aramids can decompose or char rather than melt.
Morphology alone does not guarantee a cotton cultivar, animal breed or geographic origin.
Natural fibres include plant and animal materials; regenerated fibres are manufactured from an existing polymer such as cellulose. Other manufactured fibres include several synthetic polymers. Classification is an initial task that guides subsequent examination, rather than a conclusion about the source garment.
Microscopy and Optical Characterisation
Microscopy can assess longitudinal and cross-sectional features, colour and optical properties. Refractive indices and birefringence depend on suitable preparation and interpretation.
Longitudinal microscopy examines features along a fibre; a cross-section shows shape across it. Polarised-light observations can characterise optical behaviour, including birefringence. Preparation, orientation and suitable reference material are necessary before assigning significance to those features.
Polymer Analysis: FTIR and Pyrolysis-GC-MS
Use suitable spectroscopic or thermal methods where needed. Do not declare every polymer from a single pyrolysis fragment or assume all natural fibres need no instrumental follow-up.
Dye Comparison: MSP and Chromatography
MSP and, where appropriate, chromatographic methods can compare dyes. Retain preparation and spectral conditions; similar colour or spectra need population and method context.
Textile Structure: Yarn, Weave, Fabric
Yarn twist, weave, dimensions and damage can add information. Compare relevant variation within the proposed source; a common textile design is not unique.
A yarn combines fibres and can have a recorded direction of twist. A woven fabric has interlacing yarn systems; knitted structures use interlocking loops. Construction, colour sequence, damage and a possible physical fit of torn material address different levels of comparison.
Transfer, Persistence and Fibre Collection
Transfer and persistence depend on contact, fibre properties, substrates and subsequent activity. No universal percentage or elapsed-time clock follows from finding fibres.
Collect separately with appropriate clean tools or lifts and preserve reference provenance.
Compare recovery from the relevant contact regions with separately collected reference material. Consider both direct transfer and secondary transfer, as well as shedding and later loss. The presence of a fibre describes a finding; the route and time of deposition require an activity-level assessment.
Check Your Understanding
Sources
- 1.Trace evidence analysis · New Jersey State Police
- 2.Trace Evidence Recovery Guidelines (historical technical guidance) · SWGMAT; NIST host
- 3.Fibre examiner training and thermal behaviour · SWGMAT; NIST host