Fiber Analysis

Locard Principle states ‘Whenever two objects come into contact with each other, there is always a transfer of material’. Fiber evidence can be found at crime scenes in a number of different ways, in personal contactbetween the clothing of a suspect and a victim, cross-transfers may occur. In a break-in, fiberscan become fixed to window screens, or broken glass. If a fight occurs, fibers can become fixedto a number of objects. In an auto accident, fibers, threads, or even pieces of clothing may adhereto parts of a vehicle.

Purpose: The purpose of this lab is to analyze the different characteristics of different fibers and to use this knowledge to identify an unknown fiber sample.

Safety Precautions: Be careful when burning fabric. Keep a cup of water nearby to put out your fabric scrap if necessary. Closed toed shoes and goggles must be worn

Materials:

compound light microscope
glass slide/cover slip
forceps
white paper
candle/match
sample fibers: wool, rayon, silk, polyester, cotton
unknown fiber sample

Procedure:

Part A- Microscopic Analysis: Unknown

Study the unknown fiber sample. Make a wet mount slide of the unknown fiber by using the forceps and placing it on a slide, adding a drop of water, and covering it with a cover slip.
Examine the sample using the scanning objective (4x), low power (10x), and high power (40x) on your microscope. Sketch what you see. Note any pits or striations on the fiber. Place the sketch and notes on your data table.

Part B- Microscopic Analysis: Known

Study the unknown fiber sample. Make a wet mount slide of the unknown fiber by using the forceps and placing it on a slide, adding a drop of water, and covering it with a cover slip.
Examine the sample using the scanning objective (4x), low power (10x), and high power (40x) on your microscope. Sketch what you see. Note any pits or striations on the fiber. Place the sketch and notes on your data table.
Write information on Fiber Directory.

Part C- Burn Tests

Light your candle/Bunsen burner and note the burning characteristics of each of the known fibers as well as the unknown fiber. Record your observations in the data table.
Holding the fiber in the forceps, bring it close to, but not touching the flame. Describe the fiber's behavior as it approaches the flame: does it begin to ignite, melt, or curl?
Holding the fiber in the forceps, touch the fiber to a flame: does it ignite quickly or slowly? Does it sputter, drip, or melt?
Remove the fiber from the flame and describe how it behaves: Does it self-extinguish, continue to burn, or glow?
Note any odor associated with the fiber in a flame. Does it smell like vinegar or hair?
What kind of residue it left after the fiber is removed form the flame? Does the fiber leave a white, fluffy ash, a hard bead, or a melted blob?

Part D- Your fibers

Comparing fibers from your clothing

Pick up fibers from your clothing with a piece of clear tape. Place the tape on a piece of

white paper. (Note: If you are wearing white clothing, place the tape on a sheet of dark

colored paper) Examine under a microscope.

Natural fibers tend to look like hair and will often have rough external surfaces. Plant

fibers, such as cotton, may be more ribbon shaped and may contain twists at irregular

intervals. Synthetic fibers tend to be smooth and uniform, while some may have long

extrusion lines on the outer layer.

You always leave trace fibers when you are in contact with another object. Take a piece

of clear tape and use it to pick up fibers from several places on your chair. Place the tape

on the piece of white paper near the tape with fibers from your clothing. Use the

microscope to see if you can identify fibers from your clothing that were on the chair.

Do Post Lab Questions.