8 chemical developers porous surfaces such as paper

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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.
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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.
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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 Analysis
Page 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. 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 paper, then on a glass slide. DO NOT MIX the magnetic powders and magnetic applicators! If
they are mixed, SEVERE point penalties will occur.