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Fire Scene Evidence Collection Guide

Paint

Films and Smears

Detailed Procedure:

 

To collect paint films and smears:

  1. Photograph the films/smears in place.

  2. Wet paint films or smears should be air dried before collection.

  3. Wear new, unused, clean latex or nitrile gloves.

  4. When dried films and paint smears are present on an object, the entire object should be collected with the film/smear intact. If the object is large, cut out a generous piece of the substrate around the film/smear. Do not scrape the smear off the substrate. Protect the smear with heavy paper or plastic and then place the object in a suitable rigid container, such as a box. Secure the object with ties if necessary. Continue with Step 6 below.

  5. If the item bearing the film/smear cannot be collected and the smeared portion cannot be cut out, the paint may be carefully removed from the item. Using a suitable new or properly cleaned tool (such as a putty knife), cut or pry away the FULL DEPTH of the smear or film, keeping all layers of the paint intact, from the topcoat down to the bare surface. DO NOT SCRAPE THE SURFACE OF THE PAINT OR REDUCE THE PAINT SAMPLE TO POWDER. Loosen the full depth of the smear/film down to the substrate. Place the sample in an appropriate leak-proof container such as a pillbox, glass vial, or evidence/pharmacy fold. DO NOT STICK THE SAMPLE TO ADHESIVE TAPE OR PACK IT IN COTTON. Continue with Step 6 below.

  6. Seal the container with evidence tape. Initial and date the tape.

  7. Label the container with identifying information, including case number, date, exhibit number, a brief description, and your name.

  8. Store the item in a secure location, such as a locked evidence van or your vehicle, until you are able to transport it to the laboratory.

Laboratory testing of paint films and smears:

Paint can be analyzed to determine class characteristics (color, chemical, and elemental composition). Questioned and known samples can be associated on these bases. If multiple layers of paint are present, a high degree of association may be made based on the number, sequence, and relative thickness of the layers as well as the individual characteristics of each layer. It is possible, although rare, to physically match a paint fragment to a known source based on fracture edges, surface striations, and layer structures.

Source:

Crime Scene and Evidence Collection Handbook. Bureau of Alcohol, Tobacco, Firearms and Explosives. 2005.

 

"SWGMAT Web Site." Scientific Working Group for Materials Analysis, Website, July 1, 2013.