1. Forensic Glass Analysis HC

2. http://www.videojug.com/in terview/csi-of-glass-and- light-2?autoredirect#what- are-the-different-kinds-of- glass-studied-in-csi

3. Forensic Examination of Glass Goals in examining glass evidence: –Determine the types of glass at the scene –Determine how the glass was fractured –Use physical characteristics to classify it –Individualize the glass to a source Compare physical and chemical characteristics: –Optical properties: color and refractive index –Non-optical properties: surface wear, striations from manufacturing, thickness, surface film or dirt, hardness, density –Chemical properties: additives or trace elements

4. Glass is a hard, brittle, amorphous substance that is composed of silicon oxides mixed with various metal oxides. Amorphous solids have their atoms arranged randomly, unlike crystals. WHAT IS GLASS??

5. Types of Glass Flat glass: Commonly found in doors and windows. Made by a “float glass process”; molten glass is floated on a pool of tin while cooling. Laminated glass: Used in windshields Made of two sheets of glass with plastic between them. Tempered safety glass: Used in car side windows and designed to break into tiny pieces. Tempered glass is four times stronger than window glass. Manufacture of tempered glass. Hot glass is rolled into sheets and then the upper and lower surfaces are cooled rapidly with jets of air.

6. The primary uses for glass are in windows, containers, light bulbs and eyewear. Borosilicate Glass (pyrex): 5% borax (Na 2 B 4 O 7 ) is added to resist breaking when heated or cooled. Colored Glass: metal oxides or colloidal iron (Fe) & sulfur (S) are added to change its color. Lead glass: (Crystal) Pb increases refractive index & density Types of Glass Cont’d.

7. The secret to bulletproof glass is… plastic! It’s called a laminate, and that’s a sandwich of glass, plastic, and glass, which is thicker than ordinary glass. The plastic inside the laminate is usually a polycarobnate material that’s really tough but still see-through. When a bullet is fired at a window of bulletproof glass, the bullet pierces the first layer of glass, but the plastic layer absorbs the bullet’s energy and stops it so the bullet doesn’t get through the final layer of glass. It’s not foolproof, but it’s a lot safer than regular glass! http://www.youtube.com/watch?v=h5HM3y8d0NA&safe ty_mode=true&persist_safety_mode=1&safe=active Bulletproof Glass

8. Crime Scene Clues from Glass Fracture patterns Fracture Patterns -Tell investigators whether the breakage was due to a high velocity, a low velocity bullet, or another type of projectile or object. Ex.) A bullet at high velocity produces a hole in the glass where the exit side is wider then the entry side. Low velocity bullet hole will exhibit more shattering around the hole and the hole may be irregular in shape.

9. Concoidal Fractures -Shell-like fracture patterns in the glass are the result of stress on the glass and breakage due to application of force. 2 Types Radial Fractures -Extend outward in a line from the point on the glass where the force originated Concentric Fractures: -Circular patterns around the point of origin of the force. *Label the radial and concentric fractures.

10. Radial Fractures: Concentric Fractures: Occur on the side opposite the side of impact Occur on the SAME side as the side of impact Fracture patterns allow the investigator to determine the direction of the impact on the glass.

11. -In the case of multiple fracture patterns in a single piece of glass, the sequence of events can be determined by looking closely at the radial fracture pattern. A fracture pattern will stop when it intersects with an existing fracture line. *Which pattern occurred First? Second? Third?

12. Identifying TYPES of Glass by Physical Properties 1.Density Comparisons - water displacement method - flotation method 2. Refractive Index Comparisons

13. Calculating the density of a very small piece of glass: 1. Determine its mass using a gram balance. 2.Determine the volume by filling a beaker with water In such a way as adding a single drop will cause spillage. 3. Position a graduated cylinder under the spout of the beaker. 4.Place the piece of glass into the beaker and collect the overflow water in the graduated cylinder. Measure with pipette. ***** If the fragment is large enough…simple water displacement will work. Fill a graduated cylinder to a pre-determined volume. Place glass fragment in cylinder. Measure the new volume and Subtract the original volume from this number.

14. Flotation Method -Observation that a solid particle will float in a liquid medium of greater density, sink in a liquid of lower density, or remain suspended in a liquid of equal density.

16. Refractive Index -A physical property of any material that will transmit light. -When light strikes the surface of a transparent material such as glass, it can be refracted, absorbed, or transmitted. -When light passes from one medium into another, there is a change in its direction and velocity-----Refraction. -As Light travels from one substance into a substance of greater density it SLOWS DOWN and Bends TOWARD THE NORMAL -As light travels from one substance into a substance of lesser density the light rays SPEED UP and Bend AWAY FROM THE NORMAL SEE DIAGRAM NEXT SLIDE The normal line is the line perpendicular to The boundary between the two mediums. Using Refractive Index property of glass to identify Types of glass: 1. Submersion Method 2. Snell’s Law

17. -The refractive index (n) is a ratio that compares the speed of light in a vacuum to the speed of light in the material -For example, the speed of light in water is 225,000,000 m/sec -Its refractive index can be calculated as: 3.00 x 10 8 ----speed of light in air 2.25 x 10 8 ----speed of light in water Equals--1.33 How is this useful to Forensic Investigators?

18. -If a clear material, such as glass, is immersed in a liquid that has the same refractive index, both the glass and the liquid will bend light at the same angle, and the glass will appear to Disappear Submersion method to estimate refractive index of glass:

19. Snell’s Law-A ratio of the angle of incidence to the angle of refraction as light travels from one medium to another……can be used to determine the refractive index of an unknown type of glass. Snell’s Law: (n 1 )(Sing Angle 1)=(n 2 )(Sin Angle 2) Where: n1= the refractive index of first medium n2= the refractive index of second medium Angle 1= the angle of incidence between the incoming ray and the normal line Angle 2= the angle of refraction between the outgoing ray and the normal line