A formula used by firearms and toolmark examiners to clean lead residue from bullets was found to also remove excess gun blue coating from metal cartridge cases. The formula, a mixture of acetic acid and hydrogen peroxide, works by oxidizing the coating back into solution, allowing one to determine the optimum proportion of the mixture. Acidified hydrogen peroxide formulas were also found to "clean" (oxidize or etch) metal cartridge cases in areas where there was no sebaceous latent print material or other substances that resist oxidation. Besides etching certain metals, acidified hydrogen peroxide can also decompose, producing oxygen bubbles; stirring removes bubbles that may hinder the etching process. For the concentrations considered in this experiment, the decomposition of hydrogen peroxide did not significantly deplete the amount needed for its etching action. The experiment also considered the subsequent treatment of these cleaned cartridge cases with gun blue to enhance the latent print contrast. Figures, references