Paint ToolMarks Tool Marks

Tool Marks A scratch or other microscopic marking left by the action of a tool on an object Evidentiary value: no two tool marks will be identical Ex-- Two screwdrivers made by the same manufacturer will have different imperfections on the blade. Those imperfections will show up when the tool is scraped against another object

Paint Paints are similar to fibers in that they are both forms of polymers. However, fibers are made into long strands while paints form flat sheets.

Paints are mixtures of several substances Binder- – hardens, trapping the pigments in place. – creates a protective barrier Pigments – color – Suspended – inorganic substances (Transition metals) Drying agents Delusterant- – reduce the shine – finish (or sheen) flat, egg-shell, satin, semi-gloss, high gloss. Solvent – allows paint to stay liquid – More solvent = thinner paint

Types of paint Automotive paint Structural paints Artistic paints

Forensic Uses of Paint Paint is most commonly found in the following two crimes: – Hit and Run – Burglaries Compare known and unknown paint specimens Known paint samples can be obtained from manufacturers

Physical properties Color – Problem- many objects can be painted with that same color (class characteristic) Paint layers – Very few objects or surfaces are painted with only one layer. Paint layers can be very useful as evidence. Known as color layer sequence

Sample #1 (possible) Known Sample Sample #2 (eliminated)

Fracture Matching This technique is very similar to tear matching of cloth. It is rarely used because paint chips are normally not large enough to match the edges.

Chemical Properties Solubility – A paint sample is placed in several different solvents. The amount the paint dissolves in each solvent can be compared to known standards. Chromatography – Gas Chromatograph/ Mass Spectrometer. – composition of each compound in the sample.