220 likes | 258 Views
Trace Evidence: Fibers. Fabric is the type of material and fibers are the “threads” that make up the fabric Wayne Williams. How are fibers used as evidence?. As with other trace evidence, fibers can be transferred to/from a person or objects linking them to one another.
E N D
Fabric is the type of material and fibers are the “threads” that make up the fabric • Wayne Williams
How are fibers used as evidence? • As with other trace evidence, fibers can be transferred to/from a person or objects linking them to one another.
How long do fibers persist? Most fiber evidence is lost (fall off) a short time after the transfer occurs. The fibers that do remain will be persistent.
Classification Natural • Vegetable • Animal or protein • Mineral Man-Made • Regenerated • Pure Synthetic
Natural Fibers: • Found in nature • Can be artificially colored or treated Cotton Wool Hemp
Plant Fibers Cotton - seed hairs of cotton plant • by far most common fiber(find almost everywhere) Under microscope, fibers resemble twisted ribbon Natural Fibers
Plant Fibers Linen - stem fiber from flax plant Kapok - from seed hairs of kapok plant Other fibers - Manila, hemp, sisal, jute Natural Fibers
Animal Fibers • Wool--animal fiber coming most often from sheep but may be goat (mohair,cashmere), rabbit (angora), camel, mink, beaver Wool Fibers (400X) Natural Fibers
Silk - comes from silkworm Spun as double filament (separated before use) Because of length, doesn’t shed easily Animal Fibers Natural Fibers
Mineral Fibers Asbestos - crystalline material • Used to be used for insulation • Fractures into thin rods that can get into your lungs; can kill you • Not used much anymore Natural Fibers
Manufactured Fibers Regenerated Fibers • Cellulose is dissolved, then resolidified to form the polymer fiber • Can occur in filament or staple form Example:Rayon Man-made Fibers
Synthetic Fibers • Man made • Can also be filament or staple Examples: Nylon and Polyester Man-made Fibers
Synthetic Fibers Acrylics • More common as evidence • Usually in staple form • Staples spun together, similar to wool Man-made Fibers
Threads, Yarn, Rope, Cordage Smallest component is fibers (staple) twisted together to form thread or is a filament. This thread can then be twisted with other threads to form a thicker thread (string, etc.) This thicker cord can then be twisted with other thicker cords, etc.
Filament vs. Staple Filament: Long continuous fiber (like silk) Staple: Filament is cut into smaller pieces; staples are spun together to form thread (like cotton)
Woven Fabric • Woven fabric are made by interlacing warp (lengthwise) and weft (filling) yarns. Warp run the length of the fabric and parallel to the selvage which is the edge of the fabric. Weft cross over and under the warp threads
Woven Fabric • TWILL • Create by passing the warp yarn over one to three weft yarns before going under one • Makes a diagonal weave • Design resembles a stair steps • Denim is the most obvious example
Knitted fabrics are made by interlocking loops into a specific arrangement. Knitted Fabric
Using the evidence • Begin by identifying and comparing class characteristics for unknown sample (evidence) and known sample. Known Unknown
Class characteristics Color: microscopic examination Size: length and width can be measured Shape: cross section is viewed
Man, I was nailed when those forensic guys found fibers from the kid’s math assignment in my teeth.