Test Mark
Definition
A reference mark deliberately made with a suspect tool against a soft medium (lead, clay, aluminium) so it can be compared against the questioned mark.
- Medium used
- Soft materials such as lead, clay, aluminium
- Made with
- The suspect tool itself
- Purpose
- Reference for comparison to the questioned mark
- Field
- Tool mark examination
Common questions
Why is a soft medium chosen for test marks?+
A soft, uniform surface records the tool's working edge with minimal distortion, letting the examiner capture consistent, repeatable striations that reveal the tool's individual characteristics without the noise a harder or uneven surface would add.
How many test marks does an examiner typically make?+
Multiple test marks are made at varying angles and pressures because a single mark may not capture the full range of striae the tool can produce, and comparing several improves confidence before matching against the questioned mark.
Related terms
- Class Characteristics
- Features deliberately or systematically imparted to a group of items by design or manufacture, such as the calibre of a bullet, the...
- Dynamic Mark
- A combination of compression and sliding in one contact. The most common real-world tool mark and the hardest to reproduce in test...
- Impression Mark
- A compression mark made when a tool meets a softer surface with no relative motion. Hammer face on brass, plier jaw crimping...
- Individual Characteristics
- Surface features on a fired bullet or cartridge case that arise from random or unique events (tool wear, corrosion, service damage) and...
- Striation Mark
- A scratch pattern made when a tool slides across a softer surface. Pry bar dragging across painted wood, blade cut, a screwdriver...