The vapor (fumes) of the cyanoacrylate monomer tend to polymerize more quickly on a fingerprint than on the surrounding, clean surface. The polymerization shows as a white deposit. The effectiveness of this process depends on the age of the fingerprint, the conditions to which it was subjected, and the way the fuming is done. For optimal fuming, a relatively high humidity (around 80%) is ideal. The visibility of weak prints and prints developed on non-contrasting (light-colored) surfaces can be improved with special staining solutions. Fuming with cyanoacrylate has proved to be a very effective process, especially on those surfaces that do not lend themselves to dusting with fingerprint powders (such as plastics).
Ninhydrin is the most well known and most used reagent for visualization of fingerprints on paper and other porous materials (e.g. carton, wall-paper, latex painted walls). Ninhydrin (also known as 2,2-dihydroxyindan-1,3-dione or 1,2,3-indantrione, mono hydrate) reacts with the amino acids in sweat left behind in a fingerprint. The strongly colored compound that is then formed is called Ruhemann's purple.
Due to the strong color of Ruhemann's purple the minute amounts of amino acids (and possibly other components) left behind enable the visualization of a fingerprint.
It also reacts with amine-containing compounds (mainly proteins) in blood.
Бі реагент для вологих поверхонь
Small particle reagents
SPR Black is a suspension of molybdenedisulfide powder in water with a detergent. The powder particles adhere to a fingerprint as does a fingerprint powder. The gray, shiny prints that are developed with SPR can be lifted (after drying) with Gellifters, Instant Lifters or tape. Powder suspension can be sprayed, but small articles can also be submerged in it. The SPR method has the advantage that it can be used on wet and/or dirty/greasy surfaces.
SPR White is a suspension of white powder in water with a detergent. It works similar as the "gray" SPR (see above) but provides better contrast on dark surfaces. Background staining is more pronounced with white SPR. Rinsing with water after application of white SPR is therefore advised.
Виявлення прихованих слідів рук за допомогою DFO
DFO is a reagent that (like ninhydrin) reacts with the amino acids present in fingerprints. The areas of application are the same: porous surfaces like paper, unpainted wood and the like. A fingerprint developed with DFO is less visible in white light than after treatment with ninhydrin but with green light (about 530 nm), it fluoresces strongly. The fluorescence is viewed and photographed through orange or red filter (goggles).