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CHE 113: Fingerprint POGIL

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CHE 113

How are fingerprints made visible, collected, and analyzed? ▯ Why? Fingerprints are a unique individualizing characteristic of humans. Even identical twins will have different fingerprints. Fingerprints are formed while a person is still in the womb and are due to friction of the individual in their environment. Once formed, fingerprints will hind an imprint of your skin, sometimes it’s visible, sometimes it’s not, but it is there, wait- ing to be found. ▯ Learning Outcome ▪ Students will be able to identify the difference between latent and visible prints. ▪ Studcollection.e able to distinguish between the techniques used to expose latent prints for ▪ Students will be able to analyze fingerprint patterns, using both common types and minuti- ae. ▯ New Concepts ridges are formed underneath the skin and as long as the dermal layer stays in-tion tact, the skinprints stay the same and will come back after injury. ▯ These prints are left behind as impressions into a surface or deposited as a thin film of water and oils secreted by the body. Making a print visible means react- ing with the depositions left behind. ▯ There are basic types of fingerprints as well as numerous minutiae that are used to categorize fingerprints. ▯ Prerequisites ▪ Individual vs. Class characteristics ▯ Reading Assignment Saferstein, 8 edition, pg. 406-429 ▯ ▯ ▯ ▯ Model 1 : Visible vs. Latent Prints For a given set of circumstances, the choice of the best detection techniques, or sequence of techniques, will depend on several factors that include: the nature of the surface (eg, porous, non- porous, rough or smooth); the presence of any particular contaminants (eg, blood); environmental factors (eg, whether or not the surface is or has been wet); and, the likely age of any evidential fingermarks. In any fingerprint detection sequence, heavy emphasis should be placed on optical techniques, as these are non-destructive and may significantly improve the results obtained by physical or chemical methods. Other techniques must be applied with caution, and developed prints recorded at each opportunity, as fingermarks are fragile and readily destroyed. Techniques for Visualization Collection as Examples Evidence ▯ • Dusting : suitable for hard or non- Once visualization -Any skin Latent porous surfaces only where the is complete, the surface that secreted oils will sit above the print is has come into surface and adhere the dust to photographed and contact with create a liftable print lifted with an another solid • Luminescence : some components evidence card that surface of sweat are luminescent and has tape attached to allowing the fluoresce when illuminated with a cardboard transference lasers. Also, fluorescent dyes can backing, often of natural be employed that do not require marked with the oils and sweat laser excitation. metric system scale from the • Iodine fuming or Physical body Developers (silver nitrate): suitable for a porous material where the oils have been absorbed. The iodine is believed to dissolve in the skin oils that make up the print (temporary and will fade). • Ninhydrin: suitable for a porous material where the oils have been absorbed. A Colorless compound reacts with amino acids in sweat to form a purple colored compound. • Superglue fuming: suitable for hard or non-porous surfaces only where the secreted oils can come into contact with the Cyanoacrylate ester and polymerize. The visible prints produced are white, but are often treated with a fluorescent dye to improve visibility. ▯ No need for a visualization The print is - Skin Visible
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