It's not a single chemical, but rather a variety of chemicals and techniques are used to develop fingerprints, depending on the surface and the type of print. Some common methods include cyanoacrylate fuming, ninhydrin, and silver nitrate.
Here's a breakdown of some of the most frequently used chemicals and techniques for fingerprint development:
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Cyanoacrylate Fuming (Super Glue Fuming): This technique uses cyanoacrylate, the active ingredient in super glue. The fumes react with the amino acids and other substances present in latent fingerprints to create a visible, white deposit. This works well on non-porous surfaces like glass, metal, and plastic.
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Ninhydrin: Ninhydrin reacts with amino acids present in fingerprints to produce a purple-blue compound called Ruhemann's Purple. This method is commonly used on porous surfaces like paper and cardboard.
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Silver Nitrate: Silver nitrate reacts with the sodium chloride (salt) present in sweat. When exposed to ultraviolet light, the silver chloride formed is converted to metallic silver, which appears as a dark deposit. This method is effective on porous surfaces.
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Iodine Fuming: Iodine crystals sublimate (change directly from a solid to a gas) and the iodine vapor is absorbed by oils and fats in the fingerprint, making it temporarily visible. Iodine prints fade quickly, so they need to be photographed immediately or fixed with a chemical solution.
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DFO (1,8-Diazafluoren-9-one): Similar to ninhydrin, DFO reacts with amino acids in latent fingerprints. It often produces stronger results than ninhydrin, especially on older prints, and fluoresces under certain light conditions, making it easier to photograph.
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Physical Developer: This is a silver-based solution that reacts with the insoluble components of sweat, such as fatty acids. It's particularly useful on porous items that have been wet.
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Small Particle Reagent (SPR): SPR is a suspension of fine molybdenum disulfide particles in a detergent solution. It adheres to the fatty components of fingerprint residue on wet surfaces, making the print visible. It's effective on non-porous surfaces, especially those that are wet or greasy.
The choice of which chemical or technique to use depends on several factors, including:
- The type of surface: Porous vs. non-porous.
- The age of the fingerprint: Older prints may require more sensitive techniques.
- Environmental conditions: Whether the item has been wet or exposed to extreme temperatures.
- The nature of the fingerprint residue: Sweat, blood, grease, etc.
In summary, there is no single "fingerprint development chemical". Forensic scientists employ various chemicals and techniques, carefully selected based on the specific circumstances of each case, to visualize latent fingerprints.
