Chemical Developing of Latent Prints

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Presentation transcript:

Chemical Developing of Latent Prints

Chemical Developing Iodine Fuming Silver Nitrate Ninhydrin Cyanoacrylate (super glue) Forensic Science: Fundamentals & Investigations, Chapter 6

Iodine Fuming Iodine: fumes react with natural body fats and oils in sebaceous material of a latent print temporarily absorb the iodine vapors. This results in a change in color, from clear to yellow and dark brown, until the effect fades with time. Use on porous and non-porous surfaces such as paper, index cards, magazines, and cardboard

Silver Nitrate Silver nitrate: reacts with sodium chloride (such as those salts found in sweat) to form silver chloride. NaCl + AgNO3  AgCl + NaNO3 Exposing the silver chloride (AgCl) produced by this reaction to sunlight or an ultraviolet lamp causes the silver chloride to be reduced to metallic silver, making the latent prints visible as black or dark gray traces Used on porous surfaces The students may find it amusing to learn that if you heat superglue too much it turns into cyanide gas.

Ninhydrin Ninhydrin: reacts with amino acids to produce a purple color. Ninhydrin reacts with free amines, such as lysine (amino acid) residues in fingerprint secretions and proteins sloughed off, a deep blue or purple color known as Ruhemann's purple is produced. Ninhydrin development occurs slowly at room temperature and humidity. Complete development may take 24 to 48 hours. The development process can be accelerated by increasing the temperature and humidity. Use on porous surfaces such as paper, tissue, and clothing

Cyanoacrylate/super glue Cyanoacrylate: “superglue” in it’s gaseous state, forms a hard, whitish deposit. Most liquid super glues are really either methylcyanoacrylate or ethylcyanoacrylate. Super glue reacts with the traces of amino acids, fatty acids, and proteins in the latent fingerprint and the moisture in the air to produce a visible, sticky white material. Different colored dusts may be brushed onto the image of the fingerprint, and they will cling to the sticky white chemical from which it is formed changing its color. Used on all non-porous surfaces like metal, glass, and plastic; it will sometimes work on porous surfaces too, but not as well.