# Forensic Fiber Comparison with Split-Field Microscopy and UV-Vis Spectra
What this virtual fiber microscope demonstrates
This simulator models the practical workflow behind forensic fiber comparison: describe the questioned textile fiber, compare it with a known reference, adjust focus, rotate polarizing filters, and compare the dye response with a simplified UV-Vis absorbance curve. It is designed for students learning trace evidence, not for making casework decisions.
2 fields split microscope view
380-720 nm visible spectrum range
4 classes cotton, wool, polyester, nylon
0-180° polarizer rotation
Core observations in textile fiber comparison
Measure or estimate fiber diameter while noting natural variation along the strand.
Record twist direction, surface ridges, medulla-like features, delustering particles, and cross-sectional clues when available.
Use polarized light to compare birefringence, extinction, and brightness changes under rotation.
Compare color microscopically, then use instrumental dye information when the case requires greater discrimination.
Report whether findings are consistent, different, or inconclusive; avoid wording that implies a unique garment source without support.
| Observation | What it helps answer | Limit |
|---|---|---|
| Diameter and morphology | Are the fibers physically similar? | Manufacturing variation can overlap between garments. |
| Twist and surface detail | Do natural or synthetic features agree? | Damage, stretching, and mounting can alter appearance. |
| Polarized light response | Do optical properties match? | Birefringence is class-level evidence, not a unique signature. |
| UV-Vis dye spectrum | Are colorants consistent? | Similar dyes may appear close; extraction and instrument settings matter. |
What supports consistency
Multiple independent class characteristics agree between the questioned and known fibers.
- Comparable diameter range
- Same general fiber type
- Similar polarization behavior
- Overlapping dye absorbance peaks
What supports exclusion
A clear, repeatable difference appears in a characteristic that should match for a common textile source.
- Natural versus synthetic mismatch
- Different twist or surface morphology
- Strongly different dye spectrum
- Incompatible birefringence response
# How the Simulation Model Works
The model stores a small reference database with diameter, twist direction, fiber class, birefringence, dye family, and UV-Vis absorbance points. The questioned fiber is user-configurable, so the comparison score responds to the case profile instead of a fixed classroom sample. The visual microscope view then responds to focus and polarizer angle so students can see why optical settings matter.The polarizer control is especially useful for synthetic fibers. Polyester and nylon are assigned stronger birefringence values, so their brightness changes more visibly as the polarizer rotates. Natural cotton and wool still respond, but the simulated effect is subtler. This reflects the teaching idea that molecular orientation and fiber structure affect optical behavior.The UV-Vis chart is a simplified overlay, not a replacement for a spectrophotometer. In actual trace evidence work, dye comparison may require microspectrophotometry, thin-layer chromatography, extraction chemistry, reference controls, and documented uncertainty. The chart exists to teach why two fibers that look similar under a microscope may still separate by dye chemistry.Forensic examiners must document every step of the fiber analysis process. This includes taking detailed photographs, recording measurements, and keeping a chain of custody for all physical evidence. The simulator helps students understand the importance of systematic documentation and objective comparison in forensic casework. By interacting with different settings, users can learn how light path, sample thickness, and dye concentration affect spectral curves and physical appearance.- Questioned fiber
- A fiber recovered from a scene, victim, suspect, tool, vehicle, or other item whose source is unknown.
- Known fiber
- A reference fiber collected from a textile or object for comparison against the questioned sample.
- Birefringence
- Optical behavior in which a material has different refractive indices depending on light direction or polarization.
- UV-Vis spectrum
- A plot showing how strongly a dye or material absorbs light at different wavelengths.
- Class characteristic
- A property that can associate evidence with a group of possible sources rather than one unique source.
Interpretation tip for students
A high similarity score should be read as consistency, not identity. Trace evidence is strongest when microscopy, chemistry, transfer context, persistence, recovery method, and contamination controls all point in the same direction.Keep the conclusion within the evidence
A browser microscope cannot validate a fiber match. Formal reports should describe the observations, comparison basis, limitations, and the level of support without overstating source attribution.