The primary chemical used for fingerprinting, especially for latent prints (those not readily visible), is ninhydrin.
Ninhydrin is highly effective due to its sensitivity and ease of use. It reacts with amino acids present in sweat, which are left behind in fingerprints, to produce a purple-blue compound called Ruhemann's Purple. This reaction makes the fingerprint visible.
However, ninhydrin is not the only chemical used. Other chemicals and techniques are utilized in fingerprint development, depending on the surface and the nature of the print.
Here's a breakdown of common fingerprinting chemicals and techniques:
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Ninhydrin: As mentioned, the most commonly used chemical for latent prints on porous surfaces like paper and cardboard.
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Physical Developer (PD): Used as a last resort when ninhydrin fails. It works by reacting with fatty acids and other water-insoluble components of latent fingerprints. It's often used on porous items that have been wet.
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Cyanoacrylate (Super Glue) Fuming: Though not a chemical spray, cyanoacrylate fumes react with latent fingerprint residues to create a hard, white polymer that can then be further enhanced with dyes or powders. This is commonly used on non-porous surfaces.
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Iodine Fuming: While largely replaced by ninhydrin due to its instability and impermanence, iodine fumes can still be used. Iodine crystals are heated, and the resulting vapors are absorbed by the fingerprint residue, making it temporarily visible.
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Amido Black: A protein dye stain used on porous and non-porous surfaces, particularly when blood is present. It enhances bloody fingerprints.
Therefore, while ninhydrin is the most common answer to "what chemical is used for fingerprinting," the best answer is: it depends on the situation and the type of surface being examined. Different chemical techniques work best on different types of surfaces, and some are better at revealing prints that other methods have missed.
