Forensic Lab Report

There are many different methods for developing latent fingerprints. Some work better on non-porous surfaces, while others work best developing prints on porous surfaces. Some are destructive preventing testing the object for other forensic evidence while others are non-destructive. In order to make prints visible on porous surfaces, forensic scientists use one of three methods; Silver Nitrate, Ninhydrin and Iodine fuming. These three methods are known to be the most effective ways for developing prints. Silver Nitrate is best known for developing prints on porous surfaces. Specimen on these surfaces can either be sprayed by or immersed in a diluted form of Silver Nitrate. Three variants of silver nitrate solution are used, a 1% w/v aqueous solution, a 3% w/v aqueous solution, and a 3% w/v ethanolic solution. (Makezine: Forensics Lab 8.0: Revealing Latent Fingerprints – Introduction, 2014). Then the Silver Nitrate reacts with the salt (sodium chloride) in perspiration residue found in fingerprints making insoluble silver chloride. Next the treated specimen is exposed to a UV lamp or a source of direct sunlight. The prints first become visible as a pale yellow color, but with time they …show more content…
The specimen is placed in a fuming chamber or closed space with a few iodine crystals. Heating the iodine crystals causes them to go through sublimation (from solid to gas without liquid phase). The purple iodine gas sticks to the prints on the object turning them orange. Prints developed with iodine are temporarily visible so in order to make them semi-permanently visible the object is immersed in or sprayed with a corn starch solution. The corn starch solution dyes the prints a blue-black color; the print is then photographed for documentation. Depending on storage conditions and other factors, prints treated with iodine can last from weeks to