Day 2: Tuesday 22 September

Part 3: ...and trace

Trace contact / paint

The next talk was on chemical contact traces by Owen Face, a consultant forensic scientist. Kirk was one of the great names in forensic science and in 1953 there was a great use of contact trace evidence. ' Wherever he steps whatever  he touches.......will serve as silent evidence against him'

Paint, glass and condom lubricates are useful contact trace material. Paint often comes in multi layers. Then the layers are sectioned at an angle and paint comparison done. Colour is very useful for comparisons. The eye can distinguish many shades of colour. A big change came in 1970s when micro electronics developed i.e. computers were helping more powerful microscopes. The material is embedded in resin and colours can be seen clearly. The SEM EDX then began as a useful tool, as it now was affordable by every forensic laboratory.

Not only can you identify the paint on cars, but you can tell the model and manufacturer using such tools. In the 1970s people were talking about value for money and cost and recompense. 1980s there were little need for paint analysis generally apart from hit and run accidents. Shoe marks and DNA were the main forensics types of analyses used then. Drugs were the growth field at this time set in the social context of the time.

However, train and building graffiti cause damage and is a multi million pound problem now. This is one area where paint trace analysis can help. The comparison of colours from an object and what is left in the can is not particularly helpful as what is left behind in can differs chemically from what has previously come out of it. So is it generally worth doing this analysis? The comparison between the artist's arms or clothing with the wall is a better comparison. At times 20, liquid paint can be seen to have a globular spherical shape.  Dye from evidential lipstick can chemically be compared with control lipstick, but they are rarely looked for. For minor crime the trace evidence is seldom looked at but potential is being lost. We require more thinking at the scene. FTIR can deal with lipstick traces easily. Liquid chromatography can also deal with very small quantities. Funding is also an issue as it might be nice having powerful instruments...so we need to talk and work in a multidisciplinary way with analysts. Greases from lipsticks are based on esters and can be identified. Foundation powder can be tricky. Have to be careful with fabric in situ. SEM can be used on individual fibres with foundation adhering. Shoe polish has greases which can be extracted and analysed in a similar manner…the potential areas where trace chemical analysis can be of use is endless……

The abilities of the forensic scientists should not be forgotten in the context of developing equipment.

In the afternoon there were practical training sessions from all attendees; soil, fibres and hairs.

• CHEMICAL CONTACT TRACES -Owen Facey, Consultant Forensic Scientist
• FIBRES - Dr Kelly Sheridan, LGC Forensics
• HAIRS AND WILDLIFE DNA - Deb Hopwood
• LGC Forensics & Dr Ross McEwing
• TRACE Wildlife Forensics Network, and myself….
• SOIL INFORMATION - CHARACTERISATION FOR INTELLIGENCE & EVIDENCE - Dr Lorna Dawson, Macaulay Land Use Research Institute

An excellent day was had by all. The day was rounded off with a farewell and thank you… until the next one.

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