Crystal Violet, 25 Grams Use Crystal Violet to develop latent fingerprints on the adhesive side of almost any kind of tape, e.g., Scotch, electrical, Kraft, etc. Mix the powder in water, soak the tape in the solution and rinse with running tap water. The caution about working with Crystal Violet powder or solution is that it is a very messy dye and will stain skin, clothes, floors and counter tops. It may be very difficult, if not impossible, to remove the stains from some clothing, furniture and floor covering. Crystal Violet is also often used as a "theft detection powder." The item is first VERY lightly dusted with the powder and when the item comes into contact with moisture (for example, the thief's hands), it turns dark purple and stains anything that comes into contact with it. However, this use is NOT suggested due to the messy nature of the product and the fact that the stains DO NOT come out of most surfaces. NOTE: More Info in the Long Description Shelf-life of Crystal Violet powder: indefinite. The working solution should not be kept much longer than 3-6 months. While older solutions may continue to work, the results might not be as good.