Cyanoacrylate staining solutions

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.
Product #
Basic Yellow 40, 100 ml solution in a polyethylene bottle
Basic Yellow 40, 500 ml solution (2 g/liter in ethanol), in a spray bottle
Basic Yellow 40, 25 grams in a brown glass bottle

IUPAC name: 2-[7-(diethylamino)-2-oxo-2H-1-benzopyran-3-yl]-1,3-dimethyl-1H-benzimidazolium chloride
CAS-Number: 12221-86-2 and 29556-33-0
Type: Coumarin dye
The methanesulfonate salt (mesilate) instead of  chloride is also called Basic Yellow 40 and has CAS-no. 35869-60-4. It probably works as well as the chloride in staining cyanoacrylate.

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.)
Product #
Basic Red 14, 500 ml solution (1.5 g/liter in water, 2-propanol, methyl ethyl ketone) in a spray bottle.
Basic Red 14, 500 ml solution (2 g/liter in ethanol) in a spray bottle.
Basic Red 14, 500 ml solution (1 g/l in water with detergent, CAST formulation) in a spray bottle.
Basic Red 14, 10 gram in a brown glass bottle.

2-[2-[4-[(2-cyanoethylmethylamino]phenyl]ethenyl]-1,3,3-trimethyl-3H-Indolium, chloride
CAS-Number: 12217-48-0

To make a working solution dissolve 1.5 gram [1] or 2 gram [3] Basic Red 14 in 1 litre of ethanol (or denatured ethanol.)

Our water based formula [2] is:

1.5 gram BR14
750 ml water
150 ml methyl ethyl ketone
100 ml isopropanol

References and footnotes

[1] HOSDB, Fingerprint and Footwear Forensics Newslettter, November 2007, Publication No. 59/07.
[2] Based on the Rhodamine 6G formulation described in the AFP Workshop Manual
[3] Fingerprint Visualisation Manual (CAST/Home Office 2014)

Basic Red 14 solution in erlenmeyer flask.


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).
Product #
Ardrox, 500 ml staining solution for cyanoacrylate in spray bottle

Safranin O

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 B-84100/84200 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.
Product #
Safranine O, 100 ml solution in a polyethylene bottle
Safranine O, 500 ml solution (4 g/liter in ethanol), in a spray bottle.
Name: 3,7-diamino-2,8-dimethyl-5-phenylphenazinium chloride, Basic Red 2
CAS-Number: 477-73-6
The Safranin O solutions B-84100 and B-84200 contain 4 gram Safranin O (Basic Red 2) per liter in (denatured ethanol. This concentration is too high for fluorescence staining, the fluorescence will be largely absorbed by the Safranin O now present in the cyanoacrylate (which will be faint red). Therefore, these concentrated solutions should be diluted with ethanol.
Safranin O can be used in a concentration of circa 0.1 gram (dilution 1:40) to 0.002 gram per liter (dilution 1:800). A solution of 0.1 g/l Safranin O can be made by diluting 25 ml of B-84100 or B-84200 with 975 ml of ethanol. A solution of 0.002 g/l Safranin O can be made by diluting 20 ml of the 0.1 g/l solution with 980 ml of ethanol.
Safranin O fluoresces when excited with green light (in the range of approximately 470-560 nm). It has a maximum absorption of 530 nm (in 50% ethanol).

Rhodamine 6G

Rhodamine 6G is an exceptionally strong fluorescing stain for cyanoacrylate. Like Safranine O, it fluoresces with green light. The solution B-84500 is petroleum ether-based (so inks on polyethylene bags will not run) and need not be rinsed with water after application.
Product #
Rhodamine 6G, staining solution PE based 1 ltr
Rhodamine 6G, staining solution water based 500 ml
Name: Rhodamine 6G, 2-[6-(ethylamino)-3-(ethylimino)-2,7-dimethyl-3H-xanthene-9-yl]benzoic acid ethyl ester, Basic Red 1

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.

Product #
Sudan Black staining solution, 500 ml in a stoppered polyethylene wash bottle
Sudan Black staining solution (CAST formulation with PGME), 500 ml in a stoppered polyethylene wash bottle
Sudan Black, 25 gram