Several post-cyanoacrylate dye stains or powders may be applied to improve the visualization of the developed detail . viii Chemical Developers: Porous surfaces, such as paper, are typically processed with chemicals, including ninhydrin and physical developer , to reveal latent fingerprints. These chemicals react with specific components of latent fingerprint residue, such as amino acids and salts. Ninhydrin causes fingerprints to turn a purple color, making them easily visible and they can be photographed. 1 When iodine crystals are subjected to a slight amount of heat, they vaporize rapidly and produce violet fumes. Upon contact with fatty or oily matter, the fumes are absorbed, which develops the fingerprint and it appears yellowish-brown against the background. Iodine-fumed fingerprints are not permanent and begin to fade once the fuming is stopped. Therefore, it is necessary for the operator to have a camera ready to immediately photograph the fingerprints. 8 Other Collection Methods : In addition to the methods identified above, there are many other techniques for collecting fingerprints from wet surfaces, skin, clothing, wood, and other difficult surfaces. One of these alternative methods is the use of Crystal Violet dye, which can be useful on adhesive tapes since conventional powders adhere to the entire sticky side of the tape, regardless whether a fingerprint is present or not. 1
SCI 114 – Scientific Principles of Forensic Science Laboratory Exercise 5: Fingerprint Analysis Page 4 Experiment: Analysis of an Unknown Fingerprint Objectives: To familiarize the student with the various techniques used to develop latent fingerprints and to classify and individualize a fingerprint. Safety: 1. Perform this laboratory exercise only in accordance with established John Jay College of Criminal Justice Laboratory Safety Rules practices provided during the beginning of the semester, including appropriate personal protective equipment (PPE), such as gloves and goggles. 2. Do NOT eat, drink, or chew gum in lab; always wash your hands before or after entering and exiting the laboratory. 3. Wet powder and crystal violet get very messy, and should only be done over the sink. Double-gloving is also recommended (especially for wet powder). 4. Iodine fumes are hazardous, so the iodine crystals should never be taken out of the fume hood. Your lab instructor or lab tech will demo and perform this technique. Exercise A: Fingerprinting Techniques 1. The instructor will demonstrate the lab’s fingerprint development method capabilities. The lab has access to magnetic powders, liquid developers, and fuming apparatuses. 2. Students will practice dusting for fingerprints using their own fingerprints with magnetic powders on a glass slide. DO NOT MIX the magnetic powders and magnetic applicators! If they are mixed, SEVERE point penalties will occur. 3. Perform a tape lift on the glass slide with your dusted fingerprint and apply the fingerprint to the data sheet. Also attach your paper fingerprint.
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- Fall '19