The Silver Lining in Latent Print Revelation

The use of silver nitrate (AgNO₃) to reveal latent prints is a very simple technique has been practiced by law enforcement since the 1930′s. According to the FBI website, the technique was first used in the United States to solve the 1933 kidnapping of William A. Hamm, Jr.,  President of the Theodore Hamm Brewing Company. Very simply, an aqueous solution of silver nitrate is sprayed onto a paper or cardboard surface. It is best to saturate the paper on both sides. The paper is left to dry while being exposed to sunlight or UV light. The ridge detail emerges as a silvery image. The first reaction is a precipitation silver chloride when the silver ions react chloride ions in the fingerprint residue:
Ag⁺(aq) + NO₃^-(aq) + Na⁺(aq) + Cl^-(aq) → AgCl(s) + Na⁺(aq) + NO₃^-(aq)
Under UV light the silver chloride disproportionates into elemental silver and chlorine.
2AgCl(s) → 2Ag(s) + Cl₂(g)
Evidently, the silver nitrate may destroy other residues in the print and should be only be done if no other methods such as iodine fuming or ninhydrin reaction will be attempted. Apparently, it will also permanently stain most items. In my experience, the development under a typical UV light source (254 nm) produces a pretty faint print. It is something interesting to try, nevertheless, because of its simplicity. If it comes in contact with your skin, it will stain the epidermis skin black.
http://www.executiveforensics.com/images/research/prints7.jpg

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