Detection of latent fingerprints by the use of silver nitrate

Silver nitrate has been an established agent for the detection of latent fingerprints for some 120 years, and it was one of the few reagents suitable for use on porous surfaces until ninhydrin was introduced in forensics. The method is based on the reaction of silver ions with chlorides in the fingerprints, which are visualized in brown, violet or black. The literature describes many variations of the procedure, but the information provided is often vague and imprecise. The purpose of this study was to show whether this method can also be used on modern types of paper and how it should be applied. The results of the tests showed that silver nitrate solutions do work also on modern papers, but that they cannot be recommended as a standard, because the appearance of the prints and the paper background can strongly change in the course of time. The findings also do not justify the use of methanol-containing silver nitrate solutions in contrast to the variations based on water. For reasons of occupational safety, methanol, which is classified as poisonous, should not be used. The silver nitrate method may be taken into consideration, however, e.g. after the application of ninhydin, if there are hints that the potential fingerprints are not too old, have not been affected by moisture and if there are clues that the perpetrator perspired strongly while causing the prints.