Fluorescent Whitening Agent (FWA)
Definition
An optical brightener added to synthetic fibres and paper during manufacture; fluoresces under UV-A excitation, making treated fibres and paper highly visible under ALS.
- Also called
- Optical brightener
- Applied to
- Synthetic fibres and paper during manufacture
- Excitation
- UV-A
- Forensic use
- Increases visibility of treated fibres and paper under ALS
Common questions
How does FWA presence or absence help discriminate between fibre or paper samples in a comparison?+
Manufacturers vary in whether and how much optical brightener they add, so two visually similar fibres or papers can show markedly different fluorescence intensity or hue under UV-A. This gives an additional discriminating characteristic beyond colour and morphology when comparing questioned and known samples.
Why is FWA fluorescence useful specifically on paper documents rather than only textiles?+
Different paper stocks and production batches use different brightener formulations or concentrations, so alternate light examination can reveal inconsistencies, such as an inserted page fluorescing differently from the rest of a document, that are invisible under normal or even UV-reflected light alone.
Does the absence of FWA fluorescence mean a fibre or paper sample is unusual or suspicious?+
Not on its own. Many natural fibres and some papers are manufactured without optical brighteners at all, so a non-fluorescing sample is simply consistent with that manufacturing choice; the observation only becomes meaningful when comparing a questioned item against a specific known source.
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