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Silicone Based Casting Materials

Silicone based casting material can be used to capture the surface features of a variety of impressions encountered at crime scenes.  The resulting casts preserve the details of the various marks and can be used by the Firearm and Toolmark Section for comparative examinations back at the Laboratory.  Additionally, latent prints on relatively rough surfaces and developed by powder processing can be collected by lifting with silicone based casts using a color of casting material that contrasts with the powder.

The images below show a test mark made in lead with a screwdriver tip (upper left) being cast (upper right).  This is being done in the lab to create a known sample for comparison to an evidence mark, but the casting process and resultant marks and casts are similar to what can be done at crime scenes if toolmarks are identified.  The bottom images show a cast on one stage of a comparison microscope in the Firearm and Toolmark Section and the side-by-side comparison of a question sample to a known sample.  The striations were produced from the tip of a screw driver as seen here.

a test mark being made in lead with a screwdriverthe test mark being cast

a cast on one stage of a comparison microscope and the side-by-side comparison of a question sample to a known sample