Latent prints represent the most prevalent physical evidence recovered at crime scenes. Selecting the appropriate development methodology depends on substrate porosity, environmental exposure, and the matrix of sebaceous secretions present.

1. Non-Porous Substrates: Physical vs. Vapor Phase

Smooth surfaces such as glass, glazed ceramic, and automotive finishes respond best to high-contrast magnetic flake powders applied with fiberglass or camel hair brushes. However, fragile latent impressions benefit substantially from cyanoacrylate ester vaporization.

Fuming vaporizes ethyl-2-cyanoacrylate, reacting with amino acids, fatty acids, and moisture to synthesize a durable white polycyanoacrylate deposit adhering directly to friction ridges. Subsequent staining with fluorescent dyes (such as Rhodamine 6G or RAM) and excitation via 450nm Alternate Light Source illuminates faint latent details invisible under ambient light.

2. Porous Substrates: Chemical Reagent Sequences

For paper, cardboard, and untreated wood, physical powders often produce unreadable background smudges. Forensic standards mandate sequential chemical treatment:

1. 1,2-Indanedione-Zinc: Extremely sensitive fluorescent reagent targeting amino acids; visualized under green ALS (515–535nm) with orange barrier filters.
2. Ninhydrin: Classic Ruhemann's purple reaction; optimal for older porous documents stored in dry conditions.
3. Physical Developer (PD): Aqueous silver-based reagent targeting water-insoluble sebaceous lipids; used as a terminal step after amino acid reagents.