Shattered: Forensic Glass Analysis

1. Shattered: Forensic Glass Analysis

2. Bell Work for Tuesday, October 9 2012 • Study for your test today!! • Be sure to review on your ridge characteristics!

3. Bell Work for Friday, March 14 • What are the different methods to find the type of glass from a crime scene? • How do you know the entrance and order of bullet holes in glass? (see example below)

4. Physical Measurements • Properties • Physical Properties; can be measured without changing the substance, i.e., color, density, melting point, etc... • Chemical Properties; the way a substance changes (reacts), i.e., combustion • Density

5. Physical Properties • Mass Measurements: • Density • Temperature • Light Measurements: • Color • Refractive Index • Birefringence

6. Matter; Measurement • Density • Amount of mass per unit volume • Measured in g/cm3, or g/mL

7. Matter; Measurement • Temperature - based upon standard - melting and boiling points of water: • Fahrenheit (32° - 212°) • Celsius (0° - 100°)

8. Matter; Measurement • Temperature • Algor Mortis - drop in body temperature after death. • Generally follows linear drop to ambient temperature. • Depends upon ambient temperature, insulation (clothing), body size, activity, infection, drugs, physical shape, etc. • Glaister equation (Rectal temperature) = (98.4° F - rectal temperature)/1.5 = hours elapsed since death. • decomposition raises the internal body temperature. • Can observe incr. of body temp. (closed car in sun, etc.)

9. Matter; Measurement • Temperature • Algor Mortis - drop in body temperature after death. • Rigor Mortis - muscular rigidity w/out shortening • Livor Mortis - settling of blood

10. Physical Measurements • Light Facts: • Why are gems colorful and pencils bend? Dispersion Refraction

11. Physical Measurements • The index of refraction Dispersion Refraction

12. Physical Measurements • The index of refraction (R.I.) of a substance is equal to c (the speed of light in space) divided by the speed of light in that particular substance. Substance State Refractive Index Air Gas 1.000293 Ice Solid 1.31 Water Liquid 1.33 Ethyl Alcohol Liquid 1.36 Fluorite Solid 1.43 Quartz Solid 1.54 Salt Solid 1.54 Tourmaline Solid 1.62 Garnet Solid 1.73-1.89 Cubic Zirconia Solid 2.14 - 2.20 Diamond Solid 2.41

13. Physical Measurements • Refractive Index - Birefrignence • Gases, liquids, glass and other amorphous are isotropic substances where monochromatic light propagates in all directions with equal velocity. • Crystals can be anisotropic where the speed with which monochromatic light propagates through those materials varies with crystallographic direction..(multiple RI’s) • ”Birefringence" refers to the difference between the multiple refractive indices exhibited by an optically anisotropic material.

14. Glass Analysis • Glass is found in many types of cases - burglaries and hit-and-runs. • Glass fragments easily embed in shoes and clothing of people involved in the breakage of glass. • Glass can give class characteristics • Can give individual characteristics where a piece of glass that was broken is reconstructed when fractured pieces are fit together.

15. Glass Analysis • Mostly Class evidence from: • Broken Windshield Fracture Match • Stress Marks in Broken Glass • Molotov Cocktail from Fire • Broken Bottles (from inside or outside) • Burglery • Vandalism • Comparison of Glass Fragments

16. What Is Glass? • Glass is made of silicon oxide and metal oxides • Sand and metal oxides are melted and then cooled. • Yields an amorphous liquid (liquid!). No crystal structure. • Glass flows even at room temperature (but very slowly). • Hard and Brittle http://www.glassonweb.com/glassmanual/index.php

17. How Is Glass Made? • BLOWN OR SPIN GLASS • FLOAT GLASS PROCESS • ROLLED GLASS PROECSS http://www.glassonweb.com/glassmanual/index.php

18. How Is Glass Made? • FLOAT GLASS PROCESS - ( 1959, ca. 90% of flat glass) • The raw materials (soda lime, silica sand, calcium, oxide, soda and magnesium) are weighted, mixed and melted at 1500° C. • molten glass flows from the furnace onto a bath of molten tin in a continuous ribbon (glass and the tin do not mix - the contact surface is perfectly flat. • When leaving the bath of molten tin the glass has cooled down sufficiently to pass to an annealing chamber. http://www.glassonweb.com/glassmanual/index.php

19. Bell Work for Thursday, October 11 • Take out your notebook • You will be getting tests back today • We will watch a movie to introduce soil and glass • If time remains after notes, we will start a lab. If not, we will definitely do this tomorrow 

20. Bell Work for Friday, October 12 • Pick up the article up front • Take out your notebook for notes today • We will finish our movie • After the movie, read the article and you are going to write a summary of the article and then give me your opinion of this article for a grade • Then few more notes and do a lab

21. What is Glass? • “An inorganic product of fusion which has cooled to a rigid condition without crystallizing” • Uniform amorphous solid • No specific m.p. • Softens over a temperature • range

22. 'Ordinary' sheet glass -made by passing the molten glass through rollers; process gives an almost flat finish but with distortions. -glass is used in glazing greenhouses and garden sheds where the visual distortions do not matter. Float glass (plate) Float glass gets its name from the method of production used to manufacture it. -molten glass is 'floated' onto a bed of molten tin -produces a glass which is flat and distortion free -process imparts a fluorescence to the glass [UV light]

23. Rolled Glass Float Glass Float Glass Process

24. Toughened (Safety glass) -glass is produced by applying a special treatment to ordinary float glass after it has been cut to size and finished. -treatment involves heating the glass so that it begins to soften (about 620 C) and then rapidly cooling it. -produces a glass which, if broken, breaks into small pieces without sharp edges. Laminated glass -glass is made up of a sandwich of two or more sheets of glass (or plastic), bonded together by a flexible, normally transparent material. -if cracked or broken, the flexible material is designed to hold the glass fragments in place.

25. What’s in Glass? • Network Components-Formers: SiO2, B2O3, P2O5, GeO2, V2O5, As2O3, Sb2O5 • Fluxes–Softeners [lowers melting point]: Na2O, K2O, LiO, Al2O3, B2O3, Cs2O • Stabilizers–Chemical/Corrosion Resistance: CaO, MgO, Al2O3, PbO, SrO, BaO, ZnO, ZrO

26. Major Types and Uses • Soda lime silicate glass SiO2 + Na2O / K2O + CaO / Al2O3 / MgO • Flat glass, container glass, electric light bulbs • Borosilicate glass > 5% B2O3 (replaces Na2O) Lab glassware, thermometers, cookware, sealed-beam headlights

27. Aluminosilicate glass • Higher percentage of aluminum • higher temperatures than borosilicate • Aluminoborosilicate – 50:50 Al/B • Labware, cookware, and glass fibers • Lead alkali silicate (leaded glass) • Up to 80% PbO • high refractive index • “Crystal” tableware,

28. Different glasses-domestic windows, car headlamps, light bulb glass-are produced differently from different chemistries.

29. Forensic Individualization of Glass • Flat Glass–Soda lime silicate -Rolling or Floating • Tempered: Rapid Cooling • Adds Strength • Dices when broken • Automotive windows & security windows • Float Glass floresces when excited at 254 nm.

30. Coated: Surface modification • Mirrors • Laminated: Sandwiched around plastic • Automotive windshields • Headlights: often borosilicate • Light bulbs: soda lime glass • Heat absorbing/ UV filtering • tinting • Eyeglasses: prescription lenses/photosensitive

31. Container Glass • Lower magnesium, higher sodium • Clear vs. greenish (window) • Glass Fibers • Fiberglass insulation • Alumino-borosilicate • Binder (red or yellow) to hold fibers in bundles

32. Forensic Analysis of Glass Fundamental Question: Is it Glass? • Isotropic vs. Anisotropic • Glass: Isotropic • dark when rotated under crossed polarizers • Crystalline solids and plastics: Anisotropic • Change retardation when rotated under crossed polarizers • Hardness • Solubility

33. Comparison of Physical Characteristics • Color • Flatness • Thickness • Fluorescence–Float Glass • 254 nm

34. Physical Properties • Density • Sink-Float Method • CHBr3, C2H2Br4, Sodium Polytungstate • Density Range: 2.465-2.540 g/cm3

35. When 2 substances have different RI, light passing through them produces a Becke Line A Becke line is a band or rim of light visible along a grain/crystal boundary in plane-polarized light.

37. Glass analysis is often performed using our old friend the PLM -the goal of glass analysis by PLM is to individualize an evidence glass fragment to an exemplar from a crime scene [primary or secondary]

38. Populations of Glass RIs

39. GRIM II System -automated system for matching glass RI -uses a step-heating stage and a RI liquid that varies with temperature

40. GRIM II identifies the RI match by monitoring a video image of the glass fragment in the liquid -as it is heated/cooled the contrast is measured until a minimum is reached-the match point

41. Chemical Composition – • Inductively Coupled Plasma (ICP) • SEM/EDS • Neutron Activation Analysis • X-Ray Fluorescence

42. How does Glass break? Forensic Fracture Analysis

43. Radial Begin at a point and radiate outward from point of impact -initial crack is on the side opposite the applied force

44. Concentric Motion of the projectile through the glass puts tension on the front surface of the glass, causing concentric fractures. -high-speed projectile [a rock] penetrates the glass, it leaves an exit hole larger than it's entrance hole. -helps to determine the direction on impact.

45. A determination of the direction of force in breaking a window pane: -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.

46. It’s possible to determine the bullet's direction by noting the side of the cone- shaped hole left by the bullet. -small opening is on the entrance side Bullets and Glass

47. Counting Bullet Holes Determination of the sequence of bullet holes can be made by noting the radial fractures. Radial fractures caused by the passage of a bullet stop at pre-existing fracture.

49. CLASS AND INDIVIDUAL CHARACTERISTIC EVIDENCE • Class: a group of objects or persons with characteristic physical evidence common to it • Examples include soil and hair • Individual characteristics can be identified as having originated with a particular person or source • Establishes individuality • Examples include fingerprints and footprints

50. PRESERVING FOOTWEAR AND IMPRESSIONS • Footwear prints and impressions should be photographed: • As part of the general scene • Also photograph with a scale • Dental Stone is used in casting impressions • We will use Plaster of Paris