Developing Fingerprints - Gentian Violet
Developing Fingerprints - Gentian Violet
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This technique has one purpose in life and that is to obtain fingerprints from adhesive surfaces such as duct tape, masking tape, black electrical tape and so forth. I have only found one form of tape that I was not able to get a print off of (and no I am not going to tell what it was except that it is a very uncommon type) during some testing I did. Gentian Violet, or GV, is a skin staining process. Gentian Violet is mixed by taking 1/10th of a gram of GV powder and mixing it with 100 milliliters of distilled water. You are, at least according to some technical specifications, supposed to make sure that the water has a PH of 7-8 but as long as you conduct a test with the water used and it works then this is not absolutely required.
Mix your GV solution in an appropriate container which will allow you to immerse the tape or adhesive item totally in the solution. Allow it to stay immersed for a brief period of time (usually a couple seconds is enough). The excess stain can be rinsed away (carefully) with plain water. Any prints developed at this point should be photographed. Then if needed the item can be immersed again in the solution.
Black tape, or electricians tape, poses a slight problem as the fingerprints can't normally be seen. The prints will be a dark blue-purple color. To overcome this place the tape between two sheets of photo-paper and then lightly press a warm iron over the paper. This will cause the print to be transferred to the photo paper where it can be seen. At this point the photo-paper will contain a negative image of the print (reversed) so the print must be photographed and then the negative reversed and developed.