In what sequence should chemical methods be used for developing latent fingerprints?

The sequence of using chemical methods for developing latent fingerprints is critical for achieving the best results, as different chemicals work optimally under specific conditions and may interfere with one another if not used in the appropriate order. The correct sequence starts with iodine, followed by ninhydrin, and lastly, the physical developer.

Iodine is effective for developing fingerprints on non-porous surfaces and can produce a temporary brownish stain that helps visualize latent prints. This initial step is important because iodine vapors can penetrate the oils and residues left behind by fingerprints.

Next, ninhydrin comes into play, which is particularly effective on porous surfaces like paper. When ninhydrin reacts with amino acids present in the sweat of fingerprints, it forms a purple-blue compound, making the prints more visible. This step is best performed after iodine because ninhydrin can react with iodine, potentially diminishing the quality of the print if applied first.

Lastly, the physical developer is used. It is a silver-based solution designed to enhance fingerprint visibility on porous surfaces that have been previously treated with ninhydrin or in cases where fingerprints are older or have degraded. Using it at the end allows the previous chemical reactions to develop the prints fully without interference, while