glass as an forensic evidence

1. GLASS
BY
SWEETY SHARMA
M.Phil ( course work), department of
forensic science
Punjabi university, Patiala

2. What is glass
Hard, amorphous solid
Usually transparent
Primarily composed of silica, with various amounts of
elemental oxides
Brittle
The (ASTM) defines glass as “ an inorganic
product of fusion which has cooled to a rigid
condition without crystallizing. ”

3. Glass as evidence
 Frequently encountered in various crimes such as burglary
, road accidents, murder, sexual assault , shooting
incidents, arson and vandalism.
 The chips of broken glass from a window may be lodged
in suspects shoes or garments during the act of burglary
or particles of headlight glass may be found at the hit and
run accidents.
 Thus glass forms one of the evidentiary material in may
criminal investigations.

4. Types of glasses
• Soda lime
– most common type, used for manufacturing
windows glass, bottles, containers , bulbs ,
bangles etc. common metal oxides found in this
glass are Na, Ca, Mg, Al
• Borosilicate
– Any glass having substantial amount of boron (5
% B2O3), resistant to heat, acid corrosion &
alkalies, also known as PYREX, in manufacture of
lab glass wares, thermometers, head light of
automobile

5. • Safety glass (reduce likelihood of injury 2 persons)
• Tempered – made stronger by rapid cooling & heating
of glass. Breaks into dices, with little splintering.
• Laminated – prepared by sandwiching layer of plastic
materials b/w 2 pieces of ordinary window
• Wire – single sheet of glass with meshed layer of wire.
• Colored – produced by addition of metallic oxides to
soda lime.
• Light sensitive glass- colloidal particles of silver halide.
• Silica glass- made from molten quartz

6. Nature of information obtained
• Whether the given fragment of glass did or
did not originate from particular glass
object?
• Whether the fragment of glass has come
from particular region of glass?
• Origin of fracture and impact of force ?
• Angle of projectile

7. glass fractures examination
Glass bends when a force is applied on any surfaces. When
its elasticity limit is reached the glass fractures.
• Impact fracture
Radial fractures ( primary fracture)
– Cracks, which radiate outwards from
point of impact.
– Originate on surface opposite of force.
– 3 R RULE - R – RADIAL FRACTURE, R-
RIGHT ANGLE, R- REVERSE SIDE.

8. Radial fractures

9. • Concentric fractures (secondary fracture)
– Series of broken circles around point of impact.
– Originate from opposite of radial fractures
– Glass bends on opposite side, then stretches and
breaks on side from which original blow was
applied.
– Extend from one radial fracture to another.

12. • Cone fracture - a high velocity projectile such as bullet when
penetrates the glass leaves a round crater shaped hole, surrounded by
radial and concentric cracks .
– Hole - wider on exit side - appearance of cone.
– determine point of impact & direction of impact.

13. • Rib / stress line
– Edges of broken pieces bear a number of curved
lines, termed as stress line.
– HECKLE MARKS – small straight lines on broken
edge of glass, appear perpendicular to rib marks.

14. Sequence of holes in glass
A radial fracture in glass travel for some distance,
depending upon the force of impact, but if it
meets another fracture that has been formed
earlier, it will terminate at that point.
– Consequently if fracture from one bullet are
stopped by those made by another bullet hole, it
may be deduced that the latter was made first.

16. Angle of impact
Can be determined by amount of chipping on exit side.
• Right angle- chipping evenly distributed-
symmetrical hole
• Right of glass- chipping left surface of exit
side- elliptical hole.
• Left of glass- reversed

17. Velocity and distance of firing
• High velocity bullet - circular hole - w/o much
cracking.
• From long distance – much of the velocity
will be spent , so will break the pane much in
same way as stone does.
• Close range bullet will shatter the glass due 2
muzzle blast leaving powder residsue on the
surface.

18. Fractures due to heat
• Irregular wavy pattern.
• Glass splinters will usually fall on the side of
heat.
• If heat is localized, a piece of glass
corresponding to that area will break off.

19. Backward fragmentation
• When a sheet of glass is broken, although
most of the fragments travel in direction of
the force, but many fine chips are also
thrown backwards.
• These fine chips may be found on the
clothing of perpetrator.

20. EXAMINATION

21. Physical comparison
1. Appearance
1. Type of glass

22. Physical characteristics
Density—mass divided by volume
Refractive index (RI)—the measure of light bending due to a
change in velocity when traveling from one medium to another.
R.I- velocity of light in vaccum/velocity of light in medium
Fractures
Color
Thickness
Fluorescence
Markings—striations, dimples, etc.

23. Physical measurements
• 2 parameters –
thickness and curvature
• Edge thickness – measured by micrometer.
• Curvature – measured by spherometer.
R = I² / 6h + h / 2
Where I -mean distance b/w legs of sphmtr. &
h - height of curved surface

24. Fluorescence under UV radiation
• Examination is to be done in dark room
• Glass pieces (similar thickness)-washed with
acetone - have to be exposed in UV
Radiation
• Luminescence / fluorescence property in
glass is due ionic impurities or other
elemental additives.

25. Physical matching
 Principle - No two fractures will ever be
identical over appreciable length.
1.A complimentary lateral fit along the broken
edges over a length of quarter of inch
establishes that two glass fragments were
continuous before breaking.

26.  Edges of the samples can seen with
microscope of naked eyes, which will exactly
fit into one another.
 In case of non continuous glass patterns ,
match is made by seeing manufacturing
marks, polish marks or striations marks with
the help of diffused, incident, or oblique light
or under comparison microscope of very low
magnification

27. Density of various glasses
• Glass from various sources have different
densities.
• Window glass, flat – 2.47 to 2.56
• 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 3.02

28. Density comparison by flotation
• For this method, Bromoform (d=2.89) and Bromobenzene
(d=1.52) are selected.
• The crime and control glass piece samples are to be crushed
to comparable sizes with similar shape. Each piece of glass
is briefly sketched and marked for reference to return it to
its original packet after examination.
• A cleaned and dried sample of crime glass particle is placed
in a small beaker containing bromoform. The glass will float
on the liquid surface. This indicates that the density of
the liquid is greater than that of the glass.

29. • Add , Bromobenzene, drop wise with stirring, until the particle is
exactly suspended.
• Add sample of control glass. If both the crime and the control
glass particles remain suspended in the liquid, then, their
densities are equal to each other and to that of the liquid
mixture. Particles of different densities will either sink or
float, depending on whether they are more dense or less dense
than the liquid medium.
• The density value of the particles of glass can be determined by
calculating the density/ specific gravity of the flotation mixture
using specific gravity bottle or a pycnometer

30. Density comparison by density gradient
• Principle - A standard density gradient tube is
made up of layers of two liquids, mixed in
varying proportions so that each layer has a
different density value. When completed, a
density gradient tube will usually have 6 to
10 layers, in which bottom layers have higher
density.

31. procedure
• to estimate density with accuracy, we add
small crystals of ionic salts to the column,
whose densities are known.
Heavier Liquid Density
gm/cc
Lighter Liquid Density gm/cc
1. Bromoform
2.Sym-
Tetrabromoethane
3. Methylene iodide
2.89
2.96
3.32
i. Benzene
ii Kerosene
iii Xylene
iv Nitrobenzene
v. Bromobenzene
0.875
0.80
0.88
1.20
1.52

32. Compound Density Compound Density
KF 2.48
Na2B4O710H2 O 1.73 NaCl O3 2.49
Na2C4H4O6,
2H2O
1.82 K Cl O4 2.52
K3 Fe (CN)6 1.85 Na F 2.56
K NO2 1.91 Mg SO4 2.66
K Cl 1.98 K2 Cr2 O7 2.67
K NO3 2.10 K Mn O4 2.70
NaCl 2.16 Na2Cr O4 2.72
Na NO3 2.26 Ag ClO4 2.80
KClO3 2.32

33. i)Place seven test tubes in a test tube rack.
ii)Prepare the mixtures of bromobenzene and bromoform in the
following ratios, by
pipetting out the respective liquids into the test tubes.
a) Pure bromoform-6ml (density -2.89)
b) 1 ml of bromobenzene 5 ml of bromoform
c) 2 ml of bromobenzene 4 ml of bromoform
d) 3 ml of bromobenzene 3 ml of bromoform
e) 4 ml of bromobenzene 2 ml of bromoform
f) 5 ml of bromobenzene 1 ml of bromoform
g) Pure bromobenzene-6ml (density -1.52)
•Mark off seven equal spaces-say 4 cms apart-along each of the
two glass tubes of length 30 cms and place them in the tube stand.
•Carefully add the solutions in the order listed in step (ii) in to the
tubes (Bromoform at the bottom).

34. v.With a forceps, carefully select one of the heavier crystals listed in
table C-1 and add it to one of the columns. Repeat this process until at
least seven different crystals are added to both the columns and record
them.
vi.Allow the crystals to settle for 10 minutes and measure their initial
heights from the bottom of the tubes.
vii.Carefully add the crime and control glass fragments to their
respective columns and allow the columns to stand overnight.
viii.Record the final heights of marked crystals in each column.
ix.Plot density Vs height for the marked crystals in each column.
x.Record the height of the glass particles in each column.
xi.From the graph plotted in step (ix), determine the density of the
glass particles in each column. The data of the crystals used and graphs
plotted as shown below:
a) Record of the crystals used for calibration.

35. Crystal Initial
Height
Final
Height
Crystal Initial Height Final
Height
1.
2.
3.
4.
5.
6.
7.
8.
COLUMN-1 COLUMN-2
.

36. Refractive Index
• varies with temperature as well as
wavelength of the light source.
• represented as N20
Dwhere 20 represents the
temperature at which RI is measured, and for
sodium D line. (Sodium lamp is used to
obtain monochromatic light source.)

37. refractive indices of glasses may vary
considerably
TYPES OF GLASS N20
D
Headlight glass
Television glass
Window glass
Bottles
Opthalinic lenses
Common flat glasses
1.47 -1.49
1.49 -1.51
1.51 -1.52
1.51 -1.52
1.52 -1.53
1.51 -1.53

38. Refractive index by immersion
method
• Principle - When a transparent object, such
as glass, is immersed in a liquid of same
refractive index, it will be invisible because of
the optical homogeneity of the system.

39. procedure
• (i) Place the glass fragment in a small beaker, after
cleaning and drying.
• (ii) Select suitable liquids from the following:
a) Di-n - butyl carbonate: N20
D = 1.411
b) Tri-n bytyl citrate: N20
D = 1.455
c) Alpha – bromonapthalene: N20
D = 1.658
d) Methylene iodide: N20
D = 1.742
• (iii)Add liquid of lower index than glass in sufficient quantity
to cover the glass piece

40. • (iv) Now, add in small amounts, the liquid of higher index of
refraction, until the glass becomes invisible.
• (v) Remove the sample of liquid and determine its index of
refraction using an Abbe refractometer. Abbe refractometers
are available in the measuring ranges from 1.30 to 1.70 and
from 1.45 to 1.84.

41. For
measuring the refractive index of the
liquid mixture -
Abbe refractometers

42. Liquid N20
D Liquid N20
D
Methyl alcohol 1.3288 Anisole 1.5178
Water 1.3330 Trimethylene bromide 1.5238
Acetone 1.3592 Chloro benzene 1.5250
Ethyl acetate 1.3727 Methyl iodide 1.5310
N-Hexane 1.3755 Ethylene bromide 1.5383
N-Heptane 1.3872 Clove oil 1.5430
N-Butyl alcohal 1.4022 O-Nitro toluene 1.5466
Methyl cyclo
Hexane
1.4235 Nitro benzene 1.5526
Ethylene glycol 1.4318 Tri-O-Cresyl
Phosphate
1.5582
Ethyl citrate 1.4434 Bromobenzene 1.5602

43. BECKE LINE CONCEPT
• Becke line is the contrast (halo or bright border), which outlines the
transparent irregular particle, immersed in a liquid of different
refractive index. This halo disappears, when the liquid medium and
the transparent object have the same refractive index. Thus, when
glass particles are immersed in a liquid medium, the Becke lines will
appear due to the difference in the refractive indices of the glass
and liquid. When the indices are equal, the Becke lines will
disappear and this point is known as ‘match point.’

44. • An important advantage of the Becke line is that, it not only
indicates a difference between the indices of the glass and
liquid, but also indicates, which possesses the higher value.
Thus, when the focus of the microscope is raised, the Becke
line moves towards the medium of higher refractive index
and if the focus is lowered, it moves towards the medium of
lower refractive index. This observation allows the
examiner to properly select a liquid that most closely
matches the refractive index of glass.

45. REFERENCES
•Saferstein : criminalistics, 1976, prentice hall inc., USA.
•Laboratory physics manual – forensic physics , directorate of forensic science ,
MHA, Govt. of india.
•B.S Nabar: forensic science in crime investigation , 1988, haritha graphics,
Hyderabad
•B.R. Sharma : forensic science in criminal invesigation and trials, central law
agency , allahabad.1974.
•Saferstein : Forensic science, handbook, vol. 1 , prentice hall inc. USA.

46. Thank
you