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Technical NoteSudan BlackIntroduction One of the best processes for developing latent prints on smooth or rough, nonporous surfaces contaminated with greasy or sticky substances is Sudan Black. It works best on glass, metal or plastic materials. It can be used on waxy surfaces, such as candles or wax-paper milk cartons. Sudan Black is a dye which stains the fatty components of sebaceous secretions. Besides being sensitive to grease, oils and sticky substances, it will also enhance glue-developed latent prints. We have reports that this process works very well on the inside of latex gloves. First, the gloves must be treated with glue fumes, quite a bit heavier than normal. Dip the gloves in the solution of Sudan Black for about ten seconds and rinse in water. Continue to dip for ten seconds and rinse until latent prints appear. Often, latent prints will have better contrast after the surface dries. Safety As with any new chemical process, read and understand the Material Safety Data Sheet on all of the chemicals involved. Practice normal industrial hygienic procedures of wearing lab coats, protective gloves, and goggles, if there is any risk of splashing the solution into the eyes. If the solution is going to be used for long periods of time or on large surfaces, it is recommended that it be done in a fume hood or with adequate ventilation. The process of Sudan Black is easy, inexpensive and nontoxic. It can be a bit messy so use some common sense regarding the area you are working in to make the clean up easier. Do not use this on porous or absorbent items as the entire item will be stained a dark color. This process may run inks, and interfere with blood and body fluid examinations. Mixing Instructions Place 15 grams of Sudan Black powder in a 2 liter glass beaker. Add 1 liter of denatured ethanol and stir with a plastic stirring rod. Add 500 ml of distilled water to the beaker and stir with the stirring rod. A black working solution will result. Some of the Sudan Black will not dissolve. Some will remain as particulate matter floating in the solution or will appear as sediment. Pour the solution, including any solid matter, into a clean glass bottle with a tight-fitting screw top. Label the container appropriately. The working solution has an indefinite shelf life. Processing Instructions Shake the container of Sudan Black working solution and pour a sufficient amount into a tray large enough to place the item of evidence. Soak the item for 2 to 3 minutes. Rinse the article in cool, running tap water. The solution in the tray can be poured back into the bottle to be reused. Be certain that all undissolved dye is also returned to the bottle. For large items, pour the solution over the surface, catching the run off in a tray for reuse. Rinse with cool, running tap water. Allow the item to dry at room temperature. Applying heat is not recommended. Evaluate the latent prints only after they have dried completely. Faintly developed latent prints can sometimes be enhanced by reprocessing. Latent prints developed with Sudan Black should be photographed. While it is possible to lift the prints with tape, the tape frequently does not lift the print sufficiently. Therefore, it is strongly recommended to photograph the latent prints before attempting to lift them. Additional Reading Friction Ridge Skin: Comparison and Identification of Fingerprints by James F. CowgerManual of Fingerprint Development Techniques by the British Home Office, second edition Ordering Information Catalog No. 1-0033 Sudan Black, 30 grams
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