Which development method is effective for fingerprints on non-porous surfaces?

The method of using magnetic powders is particularly effective for developing fingerprints on non-porous surfaces due to the nature of the powders themselves. Non-porous surfaces, such as glass, plastic, or metal, do not absorb moisture or oils from the skin, which are the substances left behind in latent fingerprints. Magnetic powder adheres to the residues in the fingerprint, allowing for clear visualization against the smooth surface. The ability to use a magnetic brush for application ensures precision and minimizes disruption to the fingerprint detail.

Other methods mentioned, such as ninhydrin and iodine, are primarily suited for porous surfaces where they interact with components of the fingerprint's amino acids or oils. Ninhydrin, for instance, reacts with amino acids and is useful for paper or cardboard. Iodine vapor develops prints on porous substrates but doesn't function effectively on non-porous materials. Oil-based inks, while sometimes used for capturing prints, are not a development method; they are inks applied during the process of fingerprinting.

In summary, magnetic powders excel on non-porous surfaces as the development technique, making them the appropriate choice in this context.