forc 5-8

• Fiber Number


  • Number of fibers on the clothing of a victim is important in determining actual contact
  • The greater the number, the more likely there was actual contact
• Fiber Location


  • Where fibers are found also affects value placed on association
  • Location on different areas of the body or on specific items at a crime scene could make them more or less important
• Classification of textile fiber

  • Natural fiber
  • Textile fiber
  • Synthetic Fibers/Artificial
• Cotton fiber


  Identification of less common plants increases its value as evidence
• Animal fiber


  • Wool from sheep
  • Camel
  • Alpaca
  • Cashmere
  • Mohair
• Wool fibers


  • Wool can be woven into fine cloth for suits or coarse fabric for carpet
  • Type of fabric increases its value as evidence
• Man-made Fibers


  • More than half of all fibers used in production of textile materials are man-made
  • Some man-made fibers originate from natural fibers
• Types of man-made fibers

  • Cotton
  • Wood
  • Polyester and nylon fibers
  • Acrylics
  • Vegetable
  • Mineral
  • Organic
  • Inorganic
  • Woody fibers
  • Wool Hair silk and extracted animal fibers
  • Bast fibers
  • Asbesto
  • Leaf fibers
  • Cellulosic ax Rayon
  • Non-Cellulosic ex Nylon, casein fibers and resin fibers
  • Metallic ex. Finewire filament steel wool, tinsel thread
  • Fruit or nut
  • Rayons
  • Acetates
  • Mineral ex. Glass fiber, wool, slag, wool
• Burning or Ignition Test

  1. Manner of burning

  2. Odor of fumes

  3. Color of ash

  4. Action of fumes on moisten red and blue litmus paper

  5. Effect of litmus on a piece of filter paper moistened with lead acetate
• Animal fiber


  • Burn slowly and give odor like that of burning feather
  • When removed from the flame they do not continue to burn readily
  • Fumes turn red litmus to blue
• Wool


  Odor strong, disagreeable; fumes turn lead acetate paper black or brown
• Silk


  Odor not so pungent, fumes have no effect on lead acetate paper
• Vegetable fiber


  • Burns rapidly with a flame and give off but little smoke or fumes
  • Fumes turn blue litmus red
• Fluorescent Test - (UV)

  • Picric acid + silk = Dyed
  • Picric acid + wool = Dyed
  • Picric acid + cellulosic fibers = Unchanged
  • Millon's reagent + silk = Brown
  • Millon's reagent + wool = Brown
  • Millon's reagent + cellulosic reagent = No reaction
  • Stannic chloride + cellulose = Black
• Materials and their color under UV and daylight

  • Unbleached wool = Brilliant light blue, Light yellow
  • Bleached wool = Bluish-white to bluish yellow, White
  • Bleached cotton = Light-yellow, White
  • Mercerized cotton = Light-yellow, White
  • Bleached linen = Brilliant yellowish-white, White
  • Cuprate silk = Reddish white with blue shadow, Brownish-white
  • Viscose silk = Bluish-white with blue-violet shadow, Brownish-white
  • Nitro silk = Brilliant flesh yellow, Yellowish
  • Acetate silk = Bluish violet, White
  • Natural silk = Very bright light blue, much brighter and whiter than acetate silk, White
• Microscopic Examination


  • Most reliable and best means of identifying fiber
• Chemical Analysis of fibers

  1. Staining test - the fiber is stained with picric acid, Millon's reagent, stannic chloride or iodine solution

  2. Dissolution test if the fiber is white or light colored it is treated with the following chemicals. If dyed, the fiber is first decolorized by boiling in either 1% hydrochloric acid, acetic acid or dilute potassium hydroxide.
• Reagents


  • 10% Sodium hydroxide
  • 5% oxalic acid
  • Concentrated sulfuric acid
  • Conc. And dilute Ammonium hydroxide
  • Conc. Nitric acid
• Results


  • 10% NaOH + wool = dissolved
  • 10% NaOH + cultivated silk = dissolved
  • 10% NaOH + cotton linen, wild silk, cellulose silk = undissolved
• Paint


  A liquid suspension in a solvent carrier into which white or colored pigments and a polymeric resin binder have been combined
• Paint


  • Used for protective value and/or aesthetic purposes
  • Has a wide variety of distinguishing characteristics including color, composition (oil-based, acrylic, water-based), texture and finish
• Paint evidence


  May be in the form of a chip from a dried paint surface, trace, smear, or intact on some object
• Paint evidence is most frequently involved in burglary and hit-and-run accident cases
• How paint evidence is transferred

  1. If a suspect tries to force entry, paint chips may cling to the instrument being used and fall onto the suspect's clothing

  2. If the instrument being used is painted, some of the paint may be transferred to the object being forced open

  3. Transfers of paint chips or traces are equally probable in automobile collisions
• Components of paint


  • Pigments
  • Binder
  • Solvent
  • Additives
• Binder


  Supports the medium, forms the film, and imparts characteristics of toughness, durability, and dry time
• Solvent


  Evaporates once the paint is dry
• Common paint additives


  • Suspending agents
  • Driers
  • Anti-skinning agents
  • Wetting agents
  • Anti-foaming agents
  • Coalescing agents
  • Thickeners
  • Viscosity control agents
  • Other additives
• Pigment Volume Concentration (PVC)


  The concentration of pigment by volume in a dry coating
• PVC ranges


  • High gloss enamel - 15-25% PVC
  • Semi-gloss enamel - 30-45% PVC
  • Flat paints - 50-65% PVC
• Methods of paint application

  • Brush
  • Spray (conventional, airless, electrostatic)
  • Dip
  • Flow coat
  • Roller coat
• Types of paint systems

  • Water system paint
  • Emulsion system paint
• Drying conditions for paint

  • Air dry
  • Force dry
  • Bake
• Automotive paint


  Consists of at least four coatings: electrocoat primer, primer surface, basecoat, and clearcoat
• Examining paint evidence


  1. Examine under a stereomicroscope for color, surface texture, and color layer sequence

  2. Compare questioned and known specimens side by side
• Layer sequence is very important evidence, but layer structure alone will not provide enough information to be individualized to a single source
• Tools for examining paint

  • Microscope
  • Chemical analysis (gas chromatography, infrared radiation spectrum)
• Collecting paint evidence


  1. Use tweezers, scalpel or paper to obtain paint evidence

  2. Store in paper, glass, or plastic vials

  3. If on a garment, submit the whole garment

  4. Collect control sample from nearby undamaged area
• Paint analysis was used to help convict British serial rapist Malcolm Fairley in 1985
• Serial number


  A series of numbers that is punched or pressed into a particular item to distinguish it from others of the same type