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


Chapter 15 Physical Properties: Mineralogical, Soil, Glass, and Paint Dr. J.T. Spencer Adjunct T. L. Meeks – PowerPoint PPT presentation

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

Chapter 15 Physical Properties Mineralogical,
Soil, Glass, and Paint
  • Dr. J.T. Spencer
  • Adjunct T. L. Meeks

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.

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

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
  • 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

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
  • What type of information can these types of trace
    evidence provide
  • How are paints analyzed in forensic science

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

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

  • 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

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

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

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

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
  • An intensive property
  • Varies with temperature and the light frequency

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.

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

  • 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
  • Two of the most important of these processes are
    referred to as subtractive and additive color
  • Subtractive - blending all pigments together
    yields black and the absence of any pigment yield
  • 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

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

  • The Basics

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

Structure of Glass
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

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

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

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

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
  • Radial and Concentric cracks
  • Cratering
  • Application of force

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
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.

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.

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

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.

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

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

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

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)

  • 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
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

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

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

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?

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
  • Assault - Identifying the type of rocks used as
    weapons led to the source of the rocks and
    helped locate suspects.

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

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.

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

X-ray Fluorescence
  • Can detect major elements in soil and glass
  • sometimes detects minor trace level components

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

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.

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.

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.

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

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

Pigments Prehistoric Cave Paintings
  • 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)

  • 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
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)

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
  • The organic vehicle or binders can be
    discriminated by Gas Chromatography Mass

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

1500 Forgeries
  • In 1985 a trunk containing pastels drawings by
    the modern Russian painter Larionov was
  • Larionov left Russia for France in 1915 and these
    paintings were apparently left behind and
  • When some 200 of these paintings were exhibited
    in in Germany in 1987 some questions about their
    authenticity were raised

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
  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.