Difficulties arise when there is insufficient deposited material or no suitable reagent to generate adequate contrast, particularly when the latent print is on a multicolored or dark background. More sophisticated chemical approaches developed to address this problem include spectroscopic imaging of sweat components,4 interaction with metal nanoparticles,5 reaction with secreted drug metabolites of antibody-functionalized nanoparticles,6 and deposi- tion of the strongly colored polymer (SN)x.7 For metallic objects, of which fired cartridge cases are a forensically important example, metal vapor deposition8 and the visualization by a scanning Kelvin probe9 have proved useful. An interesting counterpart to most of the above strategies is the electrodepo- sition of polypyrrole onto the clean metal surface between fingerprint ridges to generate a negative image of the finger- print deposit.10