Two researchers held each of 10 firearms for 3 minutes. Their hands were then sprayed with Ferrotrace and the ensuing impressions photographed. The marks on the hands could be attributed in each case to the parts that are made of steel that come in close contact with the hand during the grip. In addition, two tools that are not firearms, a wrench and pliers, both made of steel, were tested in a similar way. If hands are not thoroughly washed immediately after the contact, it is possible to develop the firearm's impression on the hand as long as 7 hours after the contact. The article includes a list of weapon parts that may leave metallic residues on the hands, and fine details developed by the spray. A non-metallic handgun does not develop a characteristic pattern of a handgun, but does provide a distinctive screw imprint. The PDT (pyridyl-diphenyltriazine)-based reagents disclose contact with steel objects and could thus be useful in investigating crimes where steel tools other than guns were used. Notes, figures, references