The most essential goals in the forensic examination of fibres:
- to characterize them
- to compare them to a suspect source
- To identify source of fibres/ end-use- to determine how much was made and where it was sold
What are the steps in the analysis of comparing fibres?
Determine colour of coloured fibres/ or some other distinctive morphological feature of colourless ones
Determine genus of synthetic fibres (eg. Nylon) or class of natural ones.
Device other tests to further distinguish known and questioned fibres. These tests will depend on type of fibre.
Tests for Coloured fibres when doing comparisons
- Comparison microscopy: Bright-field microscopy, polarizing microscopy and fluorescence microscopy
- Microspectrophotometry
3.TLC or HPLC
Tests for Colourless/ lightly coloured fibres when doing comparisons
- Polymer composition: Infrared microspectroscopy,
- Birefringence
- Thermal properties
- Refractive index
- Possibly fluorescence microscopy/microspectrophotometry if fibres have optical brighteners or dyes that fluoresce
What magnification does Stereomicroscope use?
Low magnification examination
What is Stereomicroscope useful for ?
Useful in searching small items of evidence or tape
Useful in recovery and manipulation of individual fibres
What part of the Stereomicroscope makes it easier to examine a large specimen?
Boom stand allows examination of large specimen
What type of light can be utilised when using the Stereomicroscope for obseravtion?
Should be equipped for observation in both transmitted and reflected light.
The polarizing microscope has features similar to the biological microscope. What are some additional features that can only be found in the polarizing microscope.
- Rotating stage
- Polarizer beneath condenser (polarizer)
- Another polarizer located above the objectives (analyzer)
- Slot for compensators
- Strain free objectives
What does the comparison microscope allow?
Allows direct comparisons of morphological features, diameter and colour
How many filters are found in the florescence microscope?
There are two sets of filters
What are types of filters are found in the florescence microscope?
- One determines the wavelength of light that reaches the specimen causing it to in turn emit light of a longer wavelength.
- The second to block the excitation light from reaching the detectors
What are florescence microscope used for in fibre analysis?
Used to look for and observe fluorescence from dyes, optical brighteners or contaminants and not to excite particular fluorochromes.
Fluorescence microscope are equipped with what kind of filters?
Equipped with broad band excitation filters-uv to violet, blue, green
How can a microscope become a hot stage microscope and which microscope is best for this?
Hot stage accessary attached to a microscope.
The hot stage fit the stage of a polarizing light microscope
What is the hot stage microscope used for?
Used to determine the melting points of materials such as fibres and glass.
How is the hot stage microscope calibrated?
Calibrated with standards from the manufacturer.
What are some benefits of UV-VIS microspectrophotometer?
- Non-destructive method
- Only needs a single fibre
How is UV-VIS microspectrophotometer useful in forensic fibre analysis?
Used in the analysis of dyes and Can distinguish colours having different spectral curves
How is Infrared microspectrophotometer useful in forensic fibre analysis?
Used to determine the polymer composition of the fibre
What does infrared microspectrophotometer consist of?
Consists of an infrared spectrophotometer with a micro sampling accessory attached
