forensic examination of glass fragments

1. 3/5/2013
saurabh bhargava
Good morning
ma’m &
frndz..
1

2. GLASS FRACTURE ANALYSIS
INTERPRETATION OF GLASS EVIDENCES
FORENSIC EXAMINATION OF GLASS
3/5/2013
Submitted to:
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Dr Sapna Sharma
Asst. Professor
Deptt. Of Genetics
M D U, Rohtak Submitted by:
Saurabh Bhargava
Roll No. 1204
M Sc Forensic Sc(2nd sem)
2
M D U, Rohtak

3. CONTENTS
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• Glass definition
• Types of glass
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• General properties of glass
• Scope of glass examination
• Types of cracks and fractures in glass samples and
their interpretation
• Forensic examination of glass samples
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4. SCOPES
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• Glass, as a physical clue, is frequently
encountered in various crimes; such as
burglary, road accidents, murder, sexual
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assaults, shooting incidents, arson and
vandalism.
• The chips of broken glass window may be
lodged in suspect’s shoes or garments during
the act of burglary/crime; particles of
headlight glass found at the crime scene may
offer clues that confirm the identity of a
suspected vehicle; glass may also be found on 4
the clothing of an alleged assailant, where a
bottle is used as weapon.

5. CONTINUE…
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• Whenever there is violence, bottles, window
pane glass, mirrors, eye glasses and other
glass objects can be accidently scattered and
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fragments of these can also adhere to the
criminal’s clothing or shoes.
• Thus, glass forms one of the evidentiary
materials in many criminal investigations.
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6. GENERAL
•Glass can be found in most localities. It is produced in a
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wide variety of forms and compositions.
•It can occur as evidence when it is broken during the
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commission of a crime.
•Broken glass fragments ranging in size from large pieces
to tiny shards may be transferred to and retained by
nearby persons or objects.
•The mere presence of fragments of glass on the clothing
of an alleged burglar in a case involving entry through a
broken window may be significant evidence if fragments
are found.
•The significance of such evidence will be enhanced if the
fragments are determined to be indistinguishable in 6all
measured properties from the broken window.

7. 3/5/2013
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PRIMARY TRANSFER
SECONDARY TRANSFER
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8. NUMBER OF GLASS FRAGMENTS THAT CAN BE
TRANSFERRED IS CONTROLLED BY A NUMBER OF
FACTORS:
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•The closer something is to the breaking glass, the
more likely it is to have glass fragments transferred to
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it.The number of fragments transferred decreases with
distance from the break (Pounds and Smalldon 1978).
•The person breaking a window will have more glass
on him or her than a bystander, and the more blows
required to break out the glass, the more glass that
will be transferred (Allen et al. 1998b).
•The number of glass fragments generated by a
break is independent of the size and thickness of the
window but increases with greater damage to the glass
(Locke and Unikowski 1992). 8

9. RECOVERY OF GLASS FRAGMENTS FROM
CLOTHES BY A FORENSIC EXAMINER DEPENDS
UPON ADDITIONAL FACTORS:
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•Less glass is retained on slick clothing, such as
nylon jackets, than on rough clothing, such as wool
sweaters.
•Wet clothing retains more glass than dry clothing.
•Glass fragments fall off clothing over time, and
larger pieces fall off before smaller pieces.
•Glass falls off faster if the person wearing the
clothing is active.
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10. GLASS
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Glass is technically defined as
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“The inorganic product of fusion which has cooled
to a rigid condition without crystallizing”.
In contrast to crystalline solids, which have an
ordered internal arrangement of atoms, the
internal structure of glass consists of a network
of atoms lacking long-range symmetry; This
condition is referred to as the vitreous, or
glassy, state
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11. • An extended, 3D network of atoms which
lacks the repeated, orderly arrangement
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typical of crystalline materials.
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• Glass is made by heating silica sand with soda
and lime--and sometimes other materials--to a
molten mass, then cooling it so quickly that
there is no time for crystals to form in the glass. 11

12. •Even though glass is a
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liquid, to us it appears solid
it is not viscous like other
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liquids, but it looks rigid.
•The viscosity is such a high
value that the amorphous
material acts like a solid.
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13. COMPONENTS
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Formers
– forms the glassy, non-crystalline structure
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fluxes
– improve melting properties but impart low
chemical resistance
• typically alkali or alkaline earth oxides
modifiers (stabilizers or intermediates)
– a material that improves stability
• typically oxides of Ca, Al, or Zn 13

14. COMPONENTS
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• Formers:
SiO2, B2O3, P2O5, GeO2, V2O5, As2O3
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• Fluxes–Softeners [lowers melting point]:
Na2O, K2O, LiO, Al2O3, B2O3, Cs2O
• Stabilizers–Chemical/Corrosion Resistance:
CaO2, MgO2, Al2O3, PbO2, SrO, BaO,
ZnO2, ZrO
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15. TYPES OF GLASS
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A)On the basis of manufacturing process:
 Ordinary sheet glass
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 Float glass(plate)
B) On the basis of composition:
 Oxide glass
 Non oxide glass
C)On the basis of market application:
 Commercial/soda lime glass
 Lead glass
 Borosilicate glass
 Laminated glass
 Tempered glass 15

16. ROLLED AND FLOAT GLASS
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17. TEMPERED AND LAMINATED GLASS
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18. BORO-SILICATE AND LEAD GLASS
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19. SOME SPECIAL TYPES OF GLASS
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• Glass fibre
• Vitreous silica
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• Alumino-silicate glass
• Alkali-barium silicate glass
• Glass ceramics
• Technical glass
• Phosphate glass
• Optical glass
• Sealing glass
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20. GLASS FRACTURE
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• When force is applied on any surface of glass
it bends but since the elasticity of glass is
limited ultimately, it gets fractured after the
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threshold force application.
• An investigator often has to decide wheather a
pane of glass was broken from outside or from
inside, wheather it was broken with a bullet or
with a blunt object.
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21. IMPACT OF FORCE ON GLASS
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e
Impact causes a pane
of glass to bulge
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– Side opposite the
impact will stretch
more & rupture first
Radial cracks are
rapidly propagated in
short segments from
the point of impact
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22. RADIAL AND CONCENTRIC CRACKS
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 Elasticity permits bending until
radial cracks form on the opposite
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side of the force
 Continued force places tension
on the front surface (force side),
forming the concentric cracks
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23. TYPES OF CRACKS
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1) Radial cracks:
 When an object has been thrown through a
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glass pane, a fracture forming a pattern
somewhat like a spider-web will be seen.
 The cracks will appear radiating outwards
from the point of impact making a star shaped
fracture known as radial fracture.
 The radial fracture originates on the surface
opposite to that on which force was applied.
 This type of fracture is always the first to
appear on glass.
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24. RADIAL AND CONCENTRIC CRACKS
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Concentric 24
Radial
fracture
fracture

25. 4 R RULE
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Ridges on Radial
cracks are at Right
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angles to the Reverse
side of impact.
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26. TYPES CONTINUE..
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2)Concentric cracks:
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 A series of broken circles originate on the surface,
on which force is being applied around the point of
impact.
 These are the secondary fractures as they always
appear after radial fractures.
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27. TYPES CONTINUE…
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3)Cone fractures:
 When a high projectile(like bullet), penetrates the
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glass, it makes a round crater shaped hole.
 It is surrounded by radial & concentric cracks.
 The hole is usually wider on the exit side and gives
appearance like a cone.
 Thus the narrower side of a cone fracture indicates
the direction from which the bullet entered. 27

28. CONE FRACTURES
Fracture by high speed projectile
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29. FRACTURE BY BULLET
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When a bullet is
travelling at high
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velocity the
opening on the
reverse side of
impact will be
larger
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30. SIGNIFICANCE AND USE OF STUDY OF GLASS
FRACTURES
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• Fracture patterns are unique;
Pieces from the broken glass pane or hole often show
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marks that are characteristics of the type of injury and
direction of force.
 If correctly interpreted, these findings gives useful
information about the object used for breaking and
velocity of breaking object.
 Fracture examinations can provide information as to the
direction of the breaking force and the sequence of30
multiple impacts.

31. DETERMINATION OF THE DIRECTION OF FORCE
IN BREAKING A WINDOW PANE:
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-direction of the rib marks
[stress marks on broken edges of
glass that are perpendicular to
one side of glass]
For radial fractures (radiating
from the center):
- the direction of the force is on
the same side as the tangential 31
parts of the rib marks

32. 3/5/2013
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PROPAGATION OF FRACTURES DUE 32
TO MULTIPLE IMPACTS

33. Which fracture occurred first?
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34. POINTS TO REMEMBER WHILE ANALYZING
GLASS FRACTURES
✓Radial cracks are formed first, commencing on the side
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of the glass opposite to the destructive force
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✓Concentric cracks occur afterward, starting on the
same side as the force
✓As the velocity of the penetrating projectile decrease,
the irregularity of the shape of the hole and of its
surrounding cracks increase
✓Fracture always terminates at the existing line fracture
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✓Stress marks occur on the edge of a radial glass
fracture.

35. CONTINUE…
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✓Stress marks run perpendicular to one edge
and parallel to the other edge of glass.
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✓Stress’ perpendicular edge is always located
opposite from which the force of impact
occurred.
✓Concentric fractures, the perpendicular end
always faces the surface on which the force
originated.
✓Radial cracks form a Right angle on the
Reverse side of the force (4 R rule).
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36. RESULTS POSSIBLE FROM LABORATORY
EXAMINATION OF GLASS
•If the pieces of broken glass can be made to fit together in
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the manner of a jig-saw puzzle, positive association can be
made.
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•Even glass fragments as small as the head of a pin can be
compared. However, even if unusual properties are present,
only a strong indication of common origin can be given, not
an absolute identification.
•If a window has been struck with a blunt instrument such
as a rock, stick or fist, it is possible to determine the side of
impact and the nature of the force involved.
•If a window has been penetrated by a bullet, it is possible
to determine the direction from which it was fired.
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•If two or more bullet holes are in close proximity, it is
possible to determine the sequence of firing

37. OBJECTIVES
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 To be able to identify, classify & individualize the
piece/pieces of glass fragments found at
suspect/victim’s clothing or at crime scene and to
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use it, if possible, as an element to aid
reconstruction of events or as an evidence to
prove/disprove…..
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38. GLASS ANALYSIS
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# Visual Inspection of
Known/ Questioned for
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Fracture Matches
# Comparison of Glass:
•Physical Properties
•Optical Properties
•Chemical Properties
# Classification of Glass into
End Use Category
# Discrimination between
glass samples 38
# Interpretation and Value
of Results

39. PROBLEM TO BE SOLVED???
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Classification:
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The ability to use some measured characteristics of a
questioned object to place it into a product use class.
Discrimination:
The ability to distinguish between two or more objects
within the same product use class.
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40. SEQUENCE OF EXAMINATION/ANALYSIS
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•First of all physical properties are assessed.
•optical properties of the specimens are
measured next.
•Chemical composition of the glass is
typically measured last.
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41. FORENSIC GLASS EXAMINATION
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•A forensic glass analysis is typically a comparison
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of two or more glass fragments in an attempt to
determine if they originated from different sources.
•These analyses require the determination of class
characteristics that may associate objects with a
group of similar objects such as containers, but
never to a single object.
•Only physically matching of two or more broken
glass fragments allows for their association with 41
each other to the exclusion of all other sources .

42. POINTS TO REMEMBER….
•Every analytical test available is not always
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performed on each specimen.
•The aim of a comparative glass analysis is to exclude
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possible sources. When a difference is detected, no
further comparison is necessary.
•It is not always possible to assess every potential
point of comparison in each glass specimen.
•A glass fragment may be too small to be analyzed
with reproducible results even when a feature is
preserved.
•Consequently, the actual tests performed on a set of
specimens depend on the size and shape of the glass
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fragment, as well as analytical considerations.

43. PLASTIC IDENTIFICATION AND SN SURFACE
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 Plastic can be eliminated by
testing for indentation by a needle
point.
 Fluorescence upon short wave
(254nm) illumination of an original
surface can detect the Sn
contamination on one side of float
glass.
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44. TABLE SALT & GLASS SAMPLE
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 Table salt can be differentiated by
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their shape; they are crystallized
particles and thus have a regular
and ordered shape unlike glass
which is amorphous and has an
irregular shape.
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45. PHYSICAL MATCHING
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This is most conclusive proof of source
correspondence, since no two fractures will
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ever be identical over any appreciable
length.
A complimentary lateral fit along the
broken edges over a length of quarter inch
(1/4) or more establishes that the two glass
fragments were continuous before
breakage.
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46. INITIAL EXAMINATION
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The physical properties used
for comparison include glass
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color, fluorescence,
thickness, surface features,
and curvature, observance
of conchoidal fracture,
determination of hardness,
reaction to a hotpoint,
microscopy.
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47. “BUGS”-DOT NUMBERS ON VEHICLE GLASS
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48. “BUGS”-DOT NUMBERS ON VEHICLE GLASS
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49. COLOR
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Materials can be added to the batch to
produce glass in practically any color.
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Impurities present in the raw materials
used to produce glass can impart
unintentional color.
Differences in color represent a change
in glass chemistry and can be used to
differentiate specimens.
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50. COLOR CONTINUE..
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Typically not possible to reliably
perform colorimetry on glass fragments
in forensic casework due to too small
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size and too low color density of
samples.
Color assessment is performed
visually against a white background in
natural light with the particle on edge.
Side-by-side comparison should be
used with similarly sized particles. 50

51. DETECTION OF CURVATURE
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An Interferometer can be used to detect
the most minimal curvature on the glass
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surface.
Curvature indicates possible sources:
•windshield
•containers
•other non-flat glass source
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52. CURVATURE:
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A spherometer is used to measure the radius
of curvature of the glass fragments having curved surface.
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The radius of curvature of the fragment is calculated
using the formulae.
R= (l2/6h)+(h/2)
Where
1 = the mean distance between the legs of
the spherometer.
h = height of the curved surface
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53. FLUORESCENCE
•fluorescence can be used as a basis to
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differentiate glass specimens.
•The glass surface that was in contact with the tin
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bath during the manufacturing procedure will
fluoresce when exposed to short-wave (~254 nm)
ultraviolet light.
•Fluorescence examinations can also be
performed using fluorescence spectroscopy on
specimens as small as 0.05 mm2 .
•Fluorescence on a glass surface will be detected
only if the surface that will fluoresce is preserved,
collected, and analyzed.
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54. THICKNESS CONSIDERATIONS
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Tempered glass is greater than
3.0 mm thick
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Vehicle side windows are typically
3.3-3.6 mm thick
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55. DENSITY
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The ratio of the mass of an object
to the volume occupied by that object
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– g/cm3 (solids); g/mL (liquids)
d = m/V
Densities of solids & liquids are
often
compared to the density of water
– sink or float 55
Varies with temperature

56. DENSITIES OF VARIOUS GLASSES
AND RELATED MATERIALS:
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Window glass, flat- 2.47 to 2.56
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Head light glass- 2.47 to 2.63
Mica- 2.6 to 3.2
Quartz- 2.65
Glass, flint- 2.9 to 5.9
Diamond- 3.01 to 3.52 56

57. GLASS DENSITY CAN BE MEASURED BY:
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 Displacement method
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 Floatation method
 Density gradient column method
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58. REFRACTION
The bending that occurs when a light
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wave passes at an angle from one
medium to another (air to glass)
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– bending occurs because the velocity
of the wave decreases
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59. REFRACTIVE INDEX (ND)
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•The ratio of the velocity of light in a
vacuum to the velocity of light in a given
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Medium
– ND (water) = 1.333
i.e light travels 1.333 time faster in
vacuum than in water
•An intensive property
•Varies with temperature and the light
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frequency

60. R I OF COMMONLY ENCOUNTERED GLASSES
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 Automobile head light 1.47 – 1.49
glass
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 Bottles 1.51 – 1.52
 Window glass 1.51 – 1.52
 Opthalmic glass 1.52 – 1.53
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61. REFRACTIVE INDEX IS THE MOST COMMONLY
MEASURED PROPERTY IN THE FORENSIC
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EXAMINATION OF GLASS FRAGMENTS BECAUSE:
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•Precise refractive indices can be measured
rapidly on the small fragments typically found in
casework.
•It can aid in the characterization of glass.
•It provides good discrimination potential.
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62. METHODS TO CALCULATE REFRECTIVE
INDICES OF QUESTIONED GLASS SAMPLES
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Immersion Methods
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Becke line method,
Dispersion staining method
Emmons Double Variation method
Automated Method
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63. DENSITY MEASUREMENTS ARE PERFORMED LESS
FREQUENTLY THAN REFRACTIVE INDEX
DETERMINATIONS BECAUSE:
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•The glass fragment must be scrupulously clean
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and free of inclusions.
•Accurate density measurements require a
sample that is two to three millimeters in
diameter.
•density measurements required the use of
hazardous liquids, such as bromoform.
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64. BECKÉ LINE METHOD (1892)
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•When the objective of the
microscope is raised (focus
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up), a bright line moves into
the direction of the material
of higher R.I.
•Once the line disappears or
doesn’t move,the R.I. of the
oil can be measured by a
refractometer.
•The Becké line is best
observed with contrast
microscopy. 64

65. OIL IMMERSION AT THE MATCH
TEMPERATURE
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66. ELEMENTAL ANALYSIS
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Glass composition analysis can be used to
differentiate between:
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glasses made by different manufacturers,
glasses from different production lines of the same
manufacturer,
glasses made over a period of time in a single
production line.
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67. GLASS COMPOSITION ANALYSIS IS PERFORMED
INFREQUENTLY BECAUSE:
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•Most methods of glass composition analysis are
destructive.
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•Most methods require glass samples larger than those
routinely encountered in forensic casework.
•Most of the instrumentation used to measure glass
composition is expensive to purchase and maintain, and
much of the instrumentation has few other applications.
•Because of the complexity of the calculations, Bayesian
statistical analysis including compositional data is
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extremely difficult to apply.

68. 3/5/2013
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DESPITE THESE DRAWBACKS, CHEMICAL ANALYSIS
REMAINS THE BEST MEANS FOR DIFFERENTIATING
GLASS SPECIMENS.
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69. TECHNIQUES USED FOR ELEMENTAL ANALYSIS
 Semi-quantitative  quantitative techniques
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techniques  neutron activation analysis
 flameless atomic absorption
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 scanning electron spectrometry
microscopy-energy  spark-source mass
dispersive spectrometry spectrometry
 X-ray fluorescence
 inductively coupled plasma-
optical emission spectrometry
 inductively coupled plasma-
mass spectrometry
 laser ablation-inductively
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coupled plasma-mass
spectrometry

70. 3/5/2013 saurabh bhargava
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