Varnish
Definition
Transparent, hard protective film made from a drying oil, resin and solvent. Cures by oxidation (oil varnish) or polymerisation (polyurethane varnish). Used to protect wood, paintings and metalwork.
- Composition
- Drying oil or resin, plus solvent
- Curing types
- Oxidative curing (oil varnish) or polymerisation (polyurethane varnish)
- Common substrates
- Wood, paintings, metalwork
- Forensic use
- Trace transfer and comparison in vehicle, furniture, and art cases
Common questions
How does varnish differ from paint for forensic comparison purposes?+
Varnish is formulated to be transparent and lacks the pigment particles that give paint its opacity and colour, so varnish comparisons rely on the resin, oil, and additive chemistry rather than pigment identification used for paint. Instrumental methods such as FTIR and pyrolysis-GC-MS target the binder chemistry in both cases.
Why does the cure mechanism of a varnish matter to an examiner?+
An oxidatively cured oil varnish keeps changing chemically for months to years as it absorbs oxygen, altering its infrared spectrum over time, while a polymerised polyurethane varnish reaches a stable chemical state relatively quickly. Knowing which mechanism applies helps an examiner judge whether a spectral difference reflects a different product or simply a different age of cure.
Related terms
- Binder
- The polymer matrix that holds pigments in place and bonds the paint to the substrate. Identifies paint type (alkyd, acrylic, polyurethane, epoxy)...
- Cross-Section Mount
- Embedding a paint chip in resin, polishing to a flat face, and viewing under reflected light at 100 to 400 times magnification...
- Lacquer
- Clear or pigmented coating that dries purely by solvent evaporation (no chemical cure). Nitrocellulose and acrylic lacquers are the classic examples. Fast...
- Paint
- Pigmented liquid coating that dries to an opaque, coloured solid film. Built from four functional components: binder, pigment, solvent (vehicle), and additives.
- PDQ (Paint Data Query)
- RCMP-maintained international automotive paint database. Stores binder, pigment and layer data for vehicle original-equipment finishes from major manufacturers. Used to narrow a...
- Pigment
- Insoluble particles that give colour and opacity. Titanium dioxide (white), iron oxides (red/brown), carbon black (black), organic colorants (blues, reds). SEM-EDX reports...
- Pyrolysis GC-MS
- Heating a tiny polymer sample (about 1 microgram) to roughly 600 to 800 degrees Celsius in an inert atmosphere, separating the volatile...