8Chemical Developers: Poroussurfaces,suchaspaper,aretypicallyprocessedwithchemicals,includingninhydrinandphysicaldeveloper,toreveallatentfingerprints.Thesechemicalsreactwithspecificcomponentsoflatentfingerprintresidue,suchasaminoacidsandsalts.Ninhydrincausesfingerprintstoturnapurplecolor,making them easily visible and they can bephotographed.1 When iodine crystalsare 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 Violetdye, 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 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.
SCI 114 –Scientific Principles of Forensic Science Laboratory Exercise 5: Fingerprint AnalysisPage 4 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. Procedure: Exercise A: Fingerprinting Techniques 1.The instructor will demonstrate the lab’s fingerprint development method capabilities. Thelab 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 paper, then on a glass slide. DO NOT MIX the magnetic powders and magnetic applicators! If they are mixed, SEVERE point penalties will occur.