Silver Nitrate Grade and Its Effect on Physical Developer Performance-A Validation Study

Silver nitrate is a critical component of the physical developer (PD) reagent. Significant increases in the cost of silver nitrate in recent years have caused the United States Secret Service's Forensic Laboratory to look for a more economical way to produce physical developer. One possible solution to this dilemma is to use a lower grade of silver nitrate, which typically has a lower cost. This study compared the quality of fingerprints produced on various paper substrates by three physical developer working solutions, each prepared using either the American Chemical Society (ACS), U.S. Pharmacopeia (USP), or technical grade of silver nitrate. It was determined that the less pure grades of silver nitrate produced approximately the same quality of fingerprints as the ACS grade, which is currently used in the authors' laboratory for making PD working solutions. In the experiments comparing PD prepared using the ACS and USP grades of silver nitrate, the ACS grade was superior only 5% of the time, whereas the USP grade was chosen 27% of the time. In the experiments comparing PD prepared using the ACS and technical grades of silver nitrate, the ACS grade was superior only 10% of the time, whereas the technical grade was selected 17% of the time. For the majority of the sample comparisons, no difference in fingerprint quality was observed. The overall conclusion was that either USP or technical grade silver nitrate can be used in place of the current, and more expensive, ACS grade of silver nitrate.