Investigation of effective forensic cleaning methods for bullet and cartridge case samples
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Bullet and cartridge case evidence may potentially link weapons and crimes through the comparison of toolmark patterns. This analysis relies on the clarity of the toolmarks and the ability of the examiner to identify patterns on the evidence. These patterns may be distorted by debris such as soil, blood, cyanoacrylate, and construction materials. Despite the potential importance of bullet and cartridge case evidence, few investigations of proper cleaning methods have been conducted. The present study was designed to examine the effects of various cleaning solutions and application methods on copper and brass bullets and cartridge cases. Additionally, this research investigated the efficacy of these cleaning protocols on the common evidence contaminants blood and cyanoacrylate. No cleaning method was found to be universally effective on both contaminant types and nondestructive to the metal surface. Ultrasonication was the most efficient application method employed when used in conjunction with an appropriate cleaning solution. Acetone proved to be safe and successful at removing heavy cyanoacrylate deposits from brass cartridge cases without damaging the metal. Although sulfuric acid removed most of the cyanoacrylate from the brass cartridge case, ultrasonication of the fumed cartridge cases in sulfuric acid caused the nickel-plated primer caps to turn black. Additionally, etching occurred when sulfuric acid was allowed to dry on the cartridge case surface. Citric acid, salt-flour-vinegar paste, Tergazyme®, and water did not effectively remove the cyanoacrylate from the cartridge cases, but the solutions were safe to use on the brass and sometimes resulted in a shinier surface. Regardless of the cleaning method employed, the bloodstained bullets retained most or all of the underlying brown tarnish. Ultrasonication with sulfuric acid was successful at removing some blood-initiated tarnishing; however, the removal of residues was not complete, making it difficult to visualize the full striation pattern. Citric Acid, Tergazyme®, and water proved to be safe to use on the copper bullets and capable of removing loose debris, but the cleaning solutions did not effectively remove the brown tarnish. Flitz® Instant Brass and Copper Tarnish Remover caused damage to both sample types by causing etching to occur on the metal surface. Additionally, the Flitz® tarnish remover caused the brass cartridge cases to turn black over time. The use of the Sunshine Polishing Cloths left light scratches on the surface of the samples, demonstrating they are not suitable for cleaning toolmark evidence.