Glass analysis


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Glass analysis

  2. 2. CONTENTS • Glass definition • Types of glass • General properties of glass • Scope of glass examination • Types of cracks and fractures in glass samples and their interpretation • Forensic examination of glass samples 1/21/2015 2 saurabhbhargava
  3. 3. SCOPES • Glass, as a physical clue, is frequently encountered in various crimes; such as burglary, road accidents, murder, sexual 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 the clothing of an alleged assailant, where a bottle is used as weapon. 1/21/2015 3 saurabhbhargava
  4. 4. CONTINUE… • Whenever there is violence, bottles, window pane glass, mirrors, eye glasses and other glass objects can be accidently scattered and 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. 1/21/2015 4 saurabhbhargava
  5. 5. •Glass can be found in most localities. It is produced in a wide variety of forms and compositions. •It can occur as evidence when it is broken during the 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 all measured properties from the broken window. GENERAL 1/21/2015 5 saurabhbhargava
  6. 6. PRIMARY TRANSFER SECONDARY TRANSFER 1/21/2015 6 saurabhbhargava
  7. 7. •The closer something is to the breaking glass, the more likely it is to have glass fragments transferred to 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). NUMBER OF GLASS FRAGMENTS THAT CAN BE TRANSFERRED IS CONTROLLED BY A NUMBER OF FACTORS: 1/21/2015 7 saurabhbhargava
  8. 8. RECOVERY OF GLASS FRAGMENTS FROM CLOTHES BY A FORENSIC EXAMINER DEPENDS UPON ADDITIONAL FACTORS: 1/21/2015 8 saurabhbhargava •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.
  9. 9. GLASS 1/21/2015 9 saurabhbhargava Glass is technically defined as “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
  10. 10. • An extended, 3D network of atoms which lacks the repeated, orderly arrangement typical of crystalline materials. • 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. 1/21/2015saurabhbhargava 10
  11. 11. •Even though glass is a liquid, to us it appears solid it is not viscous like other liquids, but it looks rigid. •The viscosity is such a high value that the amorphous material acts like a solid. 1/21/2015saurabhbhargava 11
  12. 12. COMPONENTS 1/21/2015 12 saurabhbhargava Formers – forms the glassy, non-crystalline structure 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. 13. COMPONENTS • Formers: SiO2, B2O3, P2O5, GeO2, V2O5, As2O3 • Fluxes–Softeners [lowers melting point]: Na2O, K2O, LiO, Al2O3, B2O3, Cs2O • Stabilizers–Chemical/Corrosion Resistance: CaO2, MgO2, Al2O3, PbO2, SrO, BaO, ZnO2, ZrO 1/21/2015 13 saurabhbhargava
  14. 14. TYPES OF GLASS A)On the basis of manufacturing process:  Ordinary sheet glass  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 1/21/2015 14 saurabhbhargava
  15. 15. ROLLED AND FLOAT GLASS 1/21/2015 15 saurabhbhargava
  16. 16. TEMPERED AND LAMINATED GLASS 1/21/2015 16 saurabhbhargava
  17. 17. BORO-SILICATE AND LEAD GLASS 1/21/2015 17 saurabhbhargava
  18. 18. SOME SPECIAL TYPES OF GLASS • Glass fibre • Vitreous silica • Alumino-silicate glass • Alkali-barium silicate glass • Glass ceramics • Technical glass • Phosphate glass • Optical glass • Sealing glass 1/21/2015 18 saurabhbhargava
  19. 19. GLASS FRACTURE • 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 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. 1/21/2015 19 saurabhbhargava
  20. 20. IMPACT OF FORCE ON GLASS e 1/21/2015 20 saurabhbhargava 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
  21. 21. Elasticity permits bending until radial cracks form on the opposite side of the force Continued force places tension on the front surface (force side), forming the concentric cracks RADIAL AND CONCENTRIC CRACKS 1/21/2015 21 saurabhbhargava
  22. 22. TYPES OF CRACKS 1) Radial cracks:  When an object has been thrown through a 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. 1/21/2015 22 saurabhbhargava
  23. 23. RADIAL AND CONCENTRIC CRACKS 1/21/2015 23 saurabhbhargava Radial fracture Concentric fracture
  24. 24. 4 R RULE Ridges on Radial cracks are at Right angles to the Reverse side of impact. 1/21/2015 24 saurabhbhargava
  25. 25. TYPES CONTINUE.. 2)Concentric cracks:  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. 1/21/2015 25 saurabhbhargava
  26. 26. TYPES CONTINUE… 3)Cone fractures:  When a high projectile(like bullet), penetrates the 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. 1/21/2015 26 saurabhbhargava
  27. 27. CONE FRACTURES Fracture by high speed projectile 1/21/2015saurabhbhargava 27
  28. 28. FRACTURE BY BULLET 1/21/2015 28 saurabhbhargava When a bullet is travelling at high velocity the opening on the reverse side of impact will be larger
  29. 29. SIGNIFICANCE AND USE OF STUDY OF GLASS FRACTURES • Fracture patterns are unique; Pieces from the broken glass pane or hole often show 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 of multiple impacts. 1/21/2015 29 saurabhbhargava
  30. 30. DETERMINATION OF THE DIRECTION OF FORCE IN BREAKING A WINDOW PANE: 1/21/2015 30 saurabhbhargava -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 parts of the rib marks
  31. 31. 1/21/2015saurabhbhargava 31PROPAGATION OF FRACTURES DUE TO MULTIPLE IMPACTS
  32. 32. Which fracture occurred first? 1/21/2015saurabhbhargava 32
  33. 33. POINTS TO REMEMBER WHILE ANALYZING GLASS FRACTURES 1/21/2015 33 saurabhbhargava ✓Radial cracks are formed first, commencing on the side of the glass opposite to the destructive force ✓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 ✓Stress marks occur on the edge of a radial glass fracture.
  34. 34. CONTINUE… 1/21/2015 34 saurabhbhargava ✓Stress marks run perpendicular to one edge and parallel to the other edge of glass. ✓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).
  35. 35. •If the pieces of broken glass can be made to fit together in the manner of a jig-saw puzzle, positive association can be made. •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. •If two or more bullet holes are in close proximity, it is possible to determine the sequence of firing RESULTS POSSIBLE FROM LABORATORY EXAMINATION OF GLASS 1/21/2015 35 saurabhbhargava
  36. 36. OBJECTIVES  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 use it, if possible, as an element to aid reconstruction of events or as an evidence to prove/disprove….. 1/21/2015 36 saurabhbhargava
  37. 37. # Visual Inspection of Known/ Questioned for Fracture Matches # Comparison of Glass: •Physical Properties •Optical Properties •Chemical Properties # Classification of Glass into End Use Category # Discrimination between glass samples # Interpretation and Value of Results GLASS ANALYSIS 1/21/2015 37 saurabhbhargava
  38. 38. PROBLEM TO BE SOLVED??? 1/21/2015 38 saurabhbhargava Classification: 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.
  39. 39. SEQUENCE OF EXAMINATION/ANALYSIS 1/21/2015 39 saurabhbhargava •First of all physical properties are assessed. •optical properties of the specimens are measured next. •Chemical composition of the glass is typically measured last.
  40. 40. FORENSIC GLASS EXAMINATION 1/21/2015 40 saurabhbhargava •A forensic glass analysis is typically a comparison 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 each other to the exclusion of all other sources .
  41. 41. POINTS TO REMEMBER…. 1/21/2015 41 saurabhbhargava •Every analytical test available is not always performed on each specimen. •The aim of a comparative glass analysis is to exclude 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 fragment, as well as analytical considerations.
  42. 42. PLASTIC IDENTIFICATION AND SN SURFACE 1/21/2015 42 saurabhbhargava 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.
  43. 43. TABLE SALT & GLASS SAMPLE  Table salt can be differentiated by their shape; they are crystallized particles and thus have a regular and ordered shape unlike glass which is amorphous and has an irregular shape. 1/21/2015 43 saurabhbhargava
  44. 44. PHYSICAL MATCHING 1/21/2015 44 saurabhbhargava This is most conclusive proof of source correspondence, since no two fractures will 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.
  45. 45. INITIAL EXAMINATION 1/21/2015 45 saurabhbhargava The physical properties used for comparison include glass color, fluorescence, thickness, surface features, and curvature, observance of conchoidal fracture, determination of hardness, reaction to a hotpoint, microscopy.
  46. 46. “BUGS”-DOT NUMBERS ON VEHICLE GLASS 1/21/2015 46 saurabhbhargava
  47. 47. “BUGS”-DOT NUMBERS ON VEHICLE GLASS 1/21/2015 47 saurabhbhargava
  48. 48. COLOR 1/21/2015 48 saurabhbhargava Materials can be added to the batch to produce glass in practically any color. 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.
  49. 49. COLOR CONTINUE.. 1/21/2015 49 saurabhbhargava Typically not possible to reliably perform colorimetry on glass fragments in forensic casework due to too small 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. 50. DETECTION OF CURVATURE 1/21/2015 50 saurabhbhargava An Interferometer can be used to detect the most minimal curvature on the glass surface. Curvature indicates possible sources: •windshield •containers •other non-flat glass source
  51. 51. CURVATURE: 1/21/2015 51 saurabhbhargava A spherometer is used to measure the radius of curvature of the glass fragments having curved surface. 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
  52. 52. FLUORESCENCE 1/21/2015 52 saurabhbhargava •fluorescence can be used as a basis to differentiate glass specimens. •The glass surface that was in contact with the tin 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.
  53. 53. THICKNESS CONSIDERATIONS 1/21/2015 53 saurabhbhargava Tempered glass is greater than 3.0 mm thick Vehicle side windows are typically 3.3-3.6 mm thick
  54. 54. DENSITY 1/21/2015 54 saurabhbhargava 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 Varies with temperature
  55. 55. DENSITIES OF VARIOUS GLASSES AND RELATED MATERIALS: 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 3.52 1/21/2015 55 saurabhbhargava
  56. 56. GLASS DENSITY CAN BE MEASURED BY:  Displacement method  Floatation method  Density gradient column method 1/21/2015 56 saurabhbhargava
  57. 57. REFRACTION 1/21/2015 57 saurabhbhargava 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
  58. 58. REFRACTIVE INDEX (ND) 1/21/2015 58 saurabhbhargava •The ratio of the velocity of light in a vacuum to the velocity of light in a given 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 frequency
  59. 59. R I OF COMMONLY ENCOUNTERED GLASSES 1/21/2015saurabhbhargava 59  Automobile head light glass  Bottles  Window glass  Opthalmic glass 1.47 – 1.49 1.51 – 1.52 1.51 – 1.52 1.52 – 1.53
  60. 60. REFRACTIVE INDEX IS THE MOST COMMONLY MEASURED PROPERTY IN THE FORENSIC EXAMINATION OF GLASS FRAGMENTS BECAUSE: 1/21/2015 60 saurabhbhargava •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.
  61. 61. METHODS TO CALCULATE REFRECTIVE INDICES OF QUESTIONED GLASS SAMPLES 1/21/2015 61 saurabhbhargava Immersion Methods Becke line method, Dispersion staining method Emmons Double Variation method Automated Method
  62. 62. DENSITY MEASUREMENTS ARE PERFORMED LESS FREQUENTLY THAN REFRACTIVE INDEX DETERMINATIONS BECAUSE: 1/21/2015 62 saurabhbhargava •The glass fragment must be scrupulously clean 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.
  63. 63. BECKÉ LINE METHOD (1892) 1/21/2015 63 saurabhbhargava •When the objective of the microscope is raised (focus 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. 64. OIL IMMERSION AT THE MATCH TEMPERATURE 1/21/2015 64 saurabhbhargava
  65. 65. ELEMENTAL ANALYSIS 1/21/2015 65 saurabhbhargava Glass composition analysis can be used to differentiate between: 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.
  66. 66. GLASS COMPOSITION ANALYSIS IS PERFORMED INFREQUENTLY BECAUSE: 1/21/2015 66 saurabhbhargava •Most methods of glass composition analysis are destructive. •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 extremely difficult to apply.
  68. 68. TECHNIQUES USED FOR ELEMENTAL ANALYSIS 1/21/2015saurabhbhargava 68  Semi-quantitative techniques  scanning electron microscopy-energy dispersive spectrometry  X-ray fluorescence  quantitative techniques  neutron activation analysis  flameless atomic absorption spectrometry  spark-source mass spectrometry  inductively coupled plasma- optical emission spectrometry  inductively coupled plasma- mass spectrometry  laser ablation-inductively coupled plasma-mass spectrometry