The effect of pH on electrolyte detection of fingermarks on cartridge cases and subsequent microscopic examination

Cartridge cases may contain deposited fingermarks when the firearm was loaded (http://www.nij.gov/pubs-sum/225320.htm, J Forensic Sci, 53, 2008 and 812). Cartridge cases can be individualized with microscopic examination. However, heat and friction degrades the deposited fingermark on the fired cartridge cases, if any on the surface. Also, unfired and fired cartridge cases are made of metal, which is a nonporous surface that does not retain fingermarks well (http://www.nij.gov/pubs-sum/225320.htm). This study tests the effects of pH level on fingermark clarity on brass fired and unfired cartridge cases and microscopic striation examination (MSE). Two trials were performed to determine the optimal pH in fingermark clarity for both types of cartridges. This was performed through immersion in six pH range solutions from dilutions of sulfuric acid and sodium hydroxide for 24 h for the purpose of enhancing the fingermarks on the metal. The use of the optimal neutral pH level is suggested because immersion of the cartridge cases in pH 1-3 and 3-5 affects MSE.