Chapter 15 Physical Properties: Mineralogical, Soil, Glass, and Paint

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Chapter 15Physical Properties Mineralogical,
Soil, Glass, and Paint

• Dr. J.T. Spencer
• Adjunct T. L. Meeks

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Learning Objectives

• Physical properties can be used to define key
  features of evidence.
• What is meant by chemical and physical properties
  and change
• What is meant by the intrinsic and extrinsic
  properties of substances
• What are density and viscosity and how can they
  be measured
• What are refraction, refractive index, and
  birefringence and how are they determined
• How are colors formed and perceived in additive
  and subtractive methods.

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Learning Objectives

• Soil, mineral and other aspects of forensic
  geology can provide very valuable trace forensic
  evidence.
• What is meant by forensic geology and soil
  analysis
• How can the organic and inorganic components of
  soils be analyzed
• What types of information can be derived from the
  analyses.

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Learning Objectives

• Glass and plastics are frequently encountered in
  forensic science.
• What is the composition of glass and what types
  are most often encountered
• How are the various types of glass manufactured
  and how are they distinguished
• What types of forensic analyses of glass are
  useful
• What types of information can be gained from the
  fragmentation patterns of glass
• What is a plastic and how can it be analyzed for
  forensic information

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Learning Objectives

• Recovered paint samples are often important types
  of evidence, such as automobiles and from
  clothing used during burglaries.
• What is the chemical composition of paints and
  dyes
• What type of information can these types of trace
  evidence provide
• How are paints analyzed in forensic science

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Properties of Matter

• Chemical Properties
• a characteristic of a substance that describes
  the way the substance undergoes or resists change
  to form a new substance
• Physical Properties
• a characteristic of a substance that can be
  observed without changing the substance into
  another substance

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Physical Properties

• Extensive Properties
• depend on the amount of sample
• volume, mass
• Intensive Properties
• do not depend on the amount of sample
• melting point, density

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Density

• The ratio of the mass of an object to the volume
  occupied by that object
• g/cm3 (solids) g/mL (liquids)
• d m/V
• Densities of solids liquids are often compared
  to the density of water
• sink or float
• Density gradient
• Known to vary with temperature, usually listed at
  STP

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Density

• Calculating Density
• Density by Flotation
• Density by Water Displacement
• Density by Buoyancy

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Viscosity

• Often referred to as the thickness of a liquid
• Actually the resistance to the liquid flowing

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Refraction

• The bending that occurs when a light wave passes
  at an angle from one medium to another (air to
  glass)
• bending occurs because the velocity of the wave
  decreases

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Refractive Index (ND)

• The ratio of the velocity of light in a vacuum to
  the velocity of light in a given medium
• ND (water) 1.333
• light travels 1.333 time faster in vacuum than in
  water
• An intensive property
• Varies with temperature and the light frequency

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Refractive Index Test

• Two techniques
• Snells law
• Immersion Test looking for Becke line
• the Becke line and will always occur closest to
  the substance with a higher refractive index.

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Double Refraction

• Crystals refract a beam of light into two
  different light-ray components
• extraordinary ray
• refracted (bent)
• ordinary ray
• path unchanged
• Causes a double image to be seen
• Known as birefringence
• for calcite 1.486 1.658

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Color

• Color is the way our eyes perceive different
  wavelengths of light
• Color receptors S, M, and L type cone cells
• Each color causes a different mixture of
  signals
• Two of the most important of these processes are
  referred to as subtractive and additive color
  methods.

• Subtractive - blending all pigments together
  yields black and the absence of any pigment yield
  white
• Additive - if we start with white light,
  containing all three of the primary colors. When
  we remove one of these primary colors, the
  remaining two colors add together to give us the
  perception of another different color

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Electrical Properties

• Conductivity ability to transfer heat or
  electrons
• Resistivity resists the flow of electrons
• Ductility ability to be spun into a wire
• Malleability ability to be hammered into a sheet

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Glass

• The Basics

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What is Glass?

• One of the oldest of all manufactured materials
• A simple fusion of sand, soda lime (all opaque)
• produces a transparent solid when cooled
• SiO2 (silica) is the most common example
• An extended, 3D network of atoms which lacks the
  repeated, orderly arrangement typical of
  crystalline materials
• The viscosity is such a high value that the
  amorphous material acts like a solid

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Structure of Glass
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Physical Properties

• At ordinary temp.
• internal structure resembles a fluid
• random molecular orientation
• external structure displays the hardness
  rigidity of of a solid
• Does not show a distinct melting point
• on heating gradually softens
• on cooling gradually thickens

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Physical Properties

• Common Properties that can be used in the
  identification of glass
• hardness
• density
• Refractive index
• color

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Glass Analysis

• Items made of glass have been valued for
  millennia both for their great utility and their
  aesthetic beauty.
• applications of glass include windows and
  windshields while specialty glass is used in
  medical practice, fiber optic telecommunications,
  scientific research, and art.
• Glass is primarily composed of silicon dioxide
  (silica, SiO2)
• The silica is usually combined with smaller
  amounts of other compounds to modify the
  properties of the glass in useful ways.
• Glass is actually an amorphous material a
  material that is without a regular, repeating
  crystal structure

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Glass Analysis

• Borosilicate Glass glass made to resistant
  thermal shock through the addition of boron oxide
• Soda Lime Glass most common type of glass
  created by mixing in sodium carbonate (Na2CO3),
  lime (CaO), alumina (Al2O3) and salts (NaCl)
• Laminated Glass - a piece of clear plastic or
  resin is sandwiched or laminated between two
  pieces of glass

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Forensic Characterization

• Initial Characterizations
• Simple measurements including the dimensions,
  color, density, and refractive index
• Chemical composition is more difficult
• UV and IR spectroscopy
• Inductively Coupled Plasma Mass Spectrometry
• Supplemental Characterizations
• Piecing broken glass objects back together to
  identify impact
• Examining glass patterns to identify the order of
  impacts
• Radial and Concentric cracks
• Cratering
• Application of force

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Impact Fractures

• Impact causes a pane of glass to bulge
• Side opposite the impact will stretch more
  rupture first
• Radial cracks are rapidly propagated in short
  segments from the point of impact

Concentric fracture
Applied force
Radial fracture
Concentric fracture
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Impact Fractures

• Ridges will be seen as irregularities on the
  broken edge of a radial crack
• The first step in this method is to find
• radial fractures that are within the first
• concentric fracture.
• The next step is to figure out which side of the
  fragment was facing in and which side was facing
  out. Contaminants or residues from the inside
  surface will feel different than the outside
  surface and should be very helpful in determining
  the sides.

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Impact Fractures

• Once the radial fracture is found along with the
  inside/outside determination, look at the broken
  edge of the glass. There are ridges that are
  created when the glass is struck called
  conchoidal fractures that are visible when
  looking at the fragment in profile.
• The method used to establish this
  direction is the 4R Rule Ridge lines on
  Radial fractures are at Right
  angles to the Rear.

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Four R Rule

• Exceptions
• tempered glass
• dices without forming ridges
• very small windows held tightly in frame
• cant bend or bulge appreciably
• windows broken by heat or explosion
• no point of impact

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Bullet Analysis

• If a window is broken by a bullet, it is possible
  to determine the bullet's direction by noting the
  side of the cone-shaped hole left by the bullet.
  The small opening is on the entrance side and the
  large opening is on the exit side.
• A determination of the sequence of bullet holes
  can be made by noting the radial fractures.
  Radial fractures caused by the passage of a
  bullet will stop at any pre-existing fracture.

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Mechanical Fit

• Examiner can determine that two or more pieces of
  glass were broken from the same pane or object
• Because glass is amorphous, no two glass objects
  will break the same way

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Glass Cutters

• score the surface of glass by forcing out tiny
  chips along a line
• small chips will be missing on one side of the
  pane along the break
• Cutter type cant be accurately determined
• Association to a particular cutter possible only
  when glass chips are deposited on a cutter

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Glass as Forensic Evidence

• Glass fragments recovered from clothing
• number distribution are important
• a piece of glass embedded in a shoe has low
  probative value
• many small fragments from a shirt or sweater can
  be highly significant
• Glass must be classified
• window glass vs broken bottle glass
• Individualization may be possible

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Other Classification Methods

• Microscopy
• float glass is absolutely flat
• wine glasses are slightly curved
• bottles have microscopic defects from mould
• Fluorescence
• when excited by uv radiation, many glasses
  exhibit fluorescence
• caused by heavy metals (including tin)

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Fluorescence

• Can differentiate between float and non-float
  window glass
• Can differentiate between different samples of
  float glass in some cases

(a) non-float glass or non-float side (b) float
side Sample 1 (c) float side Sample 2
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Forensic Geology

• Geology is the detailed study of the Earth and
  its materials along with the physical processes
  that act upon them.
• Minute traces of rock, minerals, and soil can
  provide unique proxy information
• Proxy indicators, as discussed in detail in
  chapter ten, are small amounts of
  identifiable material from a specific
  location that indicate with relatively
  high accuracy information about the
  site

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Forensic Geology

• What Is Soil?
• Mixture of organic and inorganic material
• May range from 100 inorganic (sand) to nearly
  100 organic (peat)
• Inorganic part is minerals
• Organic part is decayed plant and animal material
  and is sometimes called humas

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Soil Analysis

• "For example, observation shows me that you have
  been to the Wigmore Street Post-Office this
  morning, but deduction lets me know that when
  there you dispatched a telegram.
• Observation tells me that you have a little
  reddish mould adhering to your instep. Just
  opposite the Wigmore Street Office they have
  taken up the pavement and thrown up some earth,
  which lies in such a way that it is difficult to
  avoid treading in it in entering. The earth is of
  this peculiar reddish tint which is found, as far
  as I know, nowhere else in the neighbourhood...
• (From The Sign of Four by Arthur Conan
  Doyle)

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Soil Analysis

• Bulk analysis
• Density gradient
• Particle size distribution (sieving)
• Inorganic components
• Color (dissolve in water)
• Petrography - mineral analysis
• Organic components
• Liquid chromatography
• Oxygen availability
• Bacterial DNA?

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Soil Analysis

• Hit and Run - Under-fender dirt/soil deposited
  at impact with the victim was used to locate the
  car/driver also, matching the grease on the
  victim with the grease under the car provided
  supporting evidence.
• Rape - Soil on clothing of a suspected rapist
  was used to place the suspect at the crime scene
  and to eliminate the suspect's alibi.
• Murder - Soil found on murder victims used to
  determine the location of homicides, especially
  when the murder occurs in one location and the
  body is then moved. Using water-current
  measurements, bodies/objects thrown into water
  can be located and where a discovered
  body/object originally entered the water
  determined.
• Assault - Identifying the type of rocks used as
  weapons led to the source of the rocks and
  helped locate suspects.

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Soil Analysis

• Soil is frequently found on clothing, shoes, or
  tools and in the wheel wells of vehicles.
• Most soil analysis consists of comparing two or
  more samples by their mineral content, color, and
  density. The presence of pesticides and
  herbicides have also been used in soil
  comparison.

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Soil Analysis

• Microscopic fossils called diatoms were once very
  prominent on Earth, and collectively deposited to
  form a sedimentary rock called diatomaceous
  earth. Some manufacturers use diatomaceous earth
  for insulating safes, that are used to store
  valuables. Burglary crimes have been solved by
  examining white specks from suspects' hair and
  clothing to determine that the specks were
  actually diatoms that came from broken safes at
  crime scenes, and not dandruff as the suspects
  had claimed.

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Scanning Electron Microcopy

• Can detect
• Si
• Na
• Ca
• Mg
• K
• very small samples can be analyzed (50 micrograms)

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X-ray Fluorescence

• Can detect major elements in soil and glass
  samples
• sometimes detects minor trace level components

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Elemental Analysis

• Many of the trace elements enter the glass via
  trace impurities in the raw materials
• Comparison of elemental analysis of crime glass
  reference glass
• if ranges of elements overlap for every element
• indistinguishable
• if ranges of one or more elements are different
• samples are distinguishable

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Paints and Coatings

• Painted objects and surfaces are found throughout
  society today. Cars, homes, furniture, and so
  many other objects are coated on their surfaces
  with paint to provide both protection and beauty
  to the object.
• Small pieces of paint are often unwittingly
  transferred between objects during vehicle
  accidents, burglaries, robberies, assaults,
  homicides, and even from simple contact with
  freshly painted surfaces during a crime.

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Paint Composition

• Paints are opaque coatings that are typically
  made up of three components
• pigment - very tiny particles of organic and
  inorganic colored compounds that give the paint
  its characteristic hue.
• binder suspends the pigment particles and helps
  to firmly fix them to the surface.
• solvent, such as water or an organic liquid,
  provides a consistency suitable for spreading the
  paint on the surface.

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Paint Composition

• Paints are opaque coatings that are typically
  made up of three components
• dyes
• usually a soluble compound that binds directly to
  the material and does not require any medium to
  bind the colored material to the surface.

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Pigments

• OCHRE
• ? Ochre is a mineral that has been sought and
  used by humans even before homo sapiens came into
  existence
• ? It has been used as
• Body paint
• Artist paint
• Sun blocker
• Medicine (antiseptic and clotting agent)
• Possible religious symbol for blood, life, etc

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Pigments
35,00 -10,000 ybp Homo Sapiens

• Prehistoric Cave Paintings
• Pigments Used
• Charcoal, lampblack (soot) C
• Pyrolucite, MnO
• Hematite, Fe2O3
• Magnetite, Fe3O4
• Limonite, Fe2O3 H2O
• There is good evidence that in the cave
  paintings that many of the colors were a mixture
  of various pigments, and at the some sites there
  is evidence that ochre was calcined (heated) to
  get other colors

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Pigments Prehistoric Cave Paintings
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Pigments

• Mineral Pigments in Use from
• Ancient thru Medieval Times
• Hematite Magnetite
• Limonite Goethite
• Malachite Azurite
• Cinnabar Chrysocola
• Lapis Lazuli Realgar
• Orpiment Cinnabar
• Verdigris (copper acetate - Ancient Greek)
• Van Dyke Brown (17th century peat extract)

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Pigments

• Some Dye Pigments in Use from
• Ancient thru Medieval Times
• Indigo blue
• Woad blue
• Pomegranate yellow
• Madder orange yellow
• Saffron yellow orange
• Murex - purple

Note all dyes used were natural vegetable dyes
until 1856 when Perkin developed the first
aniline dye from coal tar. This was a major
achievement and the beginning of organic
chemistry
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Pigments in Forensic Geology

• Some Pigments Uses in Cosmetics
• Ancient
• Iron Oxides
• Galena PbS (eye shadow)
• Malachite (eye shadow)
• Cerrusite PbCO3
• Modern
• Titanium Dioxide (yellow)
• Iron Oxides
• Mica (pearlescent)
• Bismuth Oxychloride (pearlescent)

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Pigments in Forensic Geology

• ? Because many of the pigments are minerals
  standard geological techniques such as
  microscopy, X-ray diffraction, SEM analysis, and
  optical spectroscopy can be used to discriminate
  them
• The organic vehicle or binders can be
  discriminated by Gas Chromatography Mass
  Spectrometry

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Locard Case

• He found rice starch and magnesium sterate
  (binders?) with bismuth,, zinc oxide, iron oxide,
  Venetian red pigment
• He then found a druggist in Lyon who had mixed
  these same ingredients in a custom face powder
  for Marie Latelle
• When confronted with the evidence Gourbin
  confessed

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1500 Forgeries

• In 1985 a trunk containing pastels drawings by
  the modern Russian painter Larionov was
  discovered
• Larionov left Russia for France in 1915 and these
  paintings were apparently left behind and
  forgotten
• When some 200 of these paintings were exhibited
  in in Germany in 1987 some questions about their
  authenticity were raised

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Proper collection and preservation of paint
evidence from an automobile suspected of being
involved in hit-and-run incident. Paint that is
foreign to the suspect automobile is observed on
the hood.

1. Scrape the foreign paint as well as all
   underlying layers of paint off the cars surface
   using a clean knife or scalpel. The scraping
   must clearly show the layer structure of the
   paint.
2. Obtain a control paint sample from an adjacent
   undamaged area of the car. Again, all layers
   must be included.
3. Package each paint specimen separately in a
   proper container. A druggist fold or a vial
   makes an excellent container.
4. Label all specimen containers. Evidence
   collectors name or initials, the date, and the
   sampling location are to be shown. All items
   collected are to be described in the evidence
   collectors field notes.