What latent print development technique was superseded by the Ninhydrin/Physical Developer method?

The Ninhydrin/Physical Developer method essentially enhanced the detection of fingerprints on porous surfaces by expanding upon earlier techniques, specifically those that relied on silver nitrate. Silver nitrate was traditionally used to visualize latent prints on porous materials, but it had several limitations, including its sensitivity to light and a less effective contrast in visualization compared to the Ninhydrin method.

Ninhydrin reacts with amino acids in perspiration to create a vivid color change, significantly improving visibility and allowing for more pronounced prints to be developed. When this is combined with Physical Developer, which is particularly effective after Ninhydrin, it further enhances the recovery of prints, especially on documents that might have been wet or contaminated.

While the other techniques listed—Superglue Fuming, Spray Powder, and Fluorescent Dye—have their specific uses and advantages for different surfaces (non-porous or challenging environments), they do not directly replace the functionality and enhancement provided by the Ninhydrin/Physical Developer combination specifically for porous surfaces, which is where silver nitrate previously had dominion. Therefore, silver nitrate is the technique that the Ninhydrin/Physical Developer method has largely superseded.