Gentian Violet is a chemical substance which is utilized in forensics to detect latent fingerprints on non-porous, oily and fatty surfaces. It is the most suitable method to analyze the sticky side of tape. However, the adhesive has to be insoluble in water.
At first, the tape which is examined has to be immersed in the solution for 1-2 min and then be rinsed off with water. Only the fatty compounds of the traces will dye and thus make the latent fingerprints visible. The process can be repeated in order to intensify the color. Used solution can be reused. The now visible fingerprints should be secured photographically.
This method was developed and used for the first time in 1884 by the biologist Hans Christian Joachim Gram, and is used since then until today.
A big disadvantage of the method is that gentian violet causes cancer.
Providing a completely optical process, EVISCAN succeeds routinely in making latent fingerprints visible on tape. Thus, not only the use of cancer causing substances is avoided, but it is a one-step process which needs no pre-treatment and no coloring is required. Also, whenever EVISCAN is used, the complete documentation of the preserving process is prepared automatically.