After development with cyanoacrylate, fluorescent staining solutions can be applied to improve the contrast of weak fingerprints and those on light-colored surfaces. Application methods include spraying, dipping, dabbing, and brushing. After rinsing with water to remove excess staining solution, the object is dried and examined with a suitable light source and viewing goggles. The light source excites the fluorescence of the dye from the staining solution.
The viewing goggles should allow only the light of the fluorescence to pass and not the light used for excitation. Depending on the nature of the fingerprinted object (which should not fluoresce in the range where the dye fluoresces) and the availability of a suitable light source and filters, a choice can be made from the following staining solutions.
Basic Yellow 40
Basic Yellow 40 is an excellent dye stain for cyanoacrylate. It fluoresces under blue light (use yellow goggles/filters to view and photograph the fluorescence). The solutions can be diluted.
Can wrapper fumed with cyanoacrylate and stained with Basic Yellow 40. Excitation: 450 nm, filter: 495 nm.
Detail of can wrapper fumed with cyanoacrylate and stained with Basic Yellow 40. Excitation: 450 nm, filter: 495 nm.
Basic Red 14
Basic Red 14 is a red dye that fluoresces under green light. The background staining is somewhat stronger than that of Basic Yellow 40.
Excitation is done with green light (around 530 nm.) The camera filter that is needed should pass light above around 590 nm (red.)
Soda can fumed with cyanoacrylate and stained with BR 14.
Fluorescence of Basic Red 14 stained fingerprints. Excitation: 530 nm, fluorescence filter: 590 nm.
The fluorescence of Ardrox is induced with long wave UV. A disadvantage of Ardrox is that the fluorescence gradually disappears (over a period of months).
Cyanocrylate fumed prints on the bottom of a plastic cup. Photographed with episcopic lighting (Photography Platform System for Polight-Flare Plus 2)
Ardrox stained fingerprint (developed with cyanoacrylate). Excitation with UV (Polilight Flare), no filter on camera
Safranin O is a dye stain for cyanoacrylate that fluoresces under green light (use red goggles/filters to view and photograph the fluorescence). The solutions Safranin O are concentrated solutions that need to be diluted strongly (with ethanol) to prepare working solutions. The fluorescence is less strong than with Basic Yellow 40.
White textured plastic (PE) fumed with cyanoacrylate. Prints are neither visible with oblique light nor with episcopic lighting
White textured plastic fumed with cyanoacrylate and stained with Safranin O (diluted 1:100 with ethanol). Excitation: 530 nm, filter: OG590
Rhodamine 6G is an exceptionally strong fluorescing stain for cyanoacrylate. Like Safranine O, it fluoresces with green light. The solution Rhodamine 6G is petroleum ether-based (so inks on polyethylene bags will not run) and need not be rinsed with water after application.
Courier bag fumed with cyanoacrylate
Cyanoacrylate developed fingeprint on courier bag stained with Rhodamine 6G, petroleum ether based
Sudan Black (Solvent Black 3)
Sudan Black is a non-fluorescing dye in an ethanol/water mixture that can also be used for staining of cyanoacrylate (for example, when the surface with the prints is fluorescent, or has become fluorescent after earlier application of a fluorescent dye stain).
The cyanoacrylate is colored blue to black, depending on the degree of absorption.
Sudan black developed print on a clear plastic bag (PE)