1. Warm-Up After attending a gallery opening Slylock has his assistant speak to the gallery and tell them one painting is a fake. Why does Slylock Fox suspect this painting is a fake?

2. Glass Evidence

3. Forensic Science: Fundamentals & Investigations, Chapter 14 3 History of Glass  The earliest human-made glass objects (beads) date back to about 2500 B.C. Egypt.  Specialized glass production was an art, a science, and a state secret in the republic of Venice over a span of hundreds of years.  By the fourteenth century, the knowledge of glass production spread throughout Europe.  The industrial revolution brought the mass production of many kinds of glass.

4. Characteristics of Glass Hard, amorphous solid Usually transparent Primarily composed of silica, with various amounts of elemental oxides Brittle Exhibits conchoidal fracture

5. What’s in Glass? Formers (bulk of glass, form glassy, non- crystalline structure): SiO 2, B 2 O 3, P 2 O 5, GeO 2, V 2 O 5, As 2 O 3, Sb 2 O 5 Fluxes (lowers melting point): Na 2 O, K 2 O, LiO, Al 2 O 3, B 2 O 3, Cs 2 O Stabilizers (Strengthen the glass and make it resistant to water and corrosion): CaO, MgO, Al 2 O 3, PbO, SrO, BaO, ZnO, ZrO

6. How is glass made? http://science.howstuffworks.com/innovation /28024-some-assembly-required-how-glass-is- made-video.htm http://science.howstuffworks.com/innovation /28024-some-assembly-required-how-glass-is- made-video.htm 6

7. Composition of Glass (continued) The raw materials for making glass are all oxides – The composition of any sample can be given in terms of the percent of each oxide used to make it – Example: the approximate composition of window or bottle glass is Silica (SiO 2 ) – 73.6 % Soda (Na 2 O) – 16.0 % Lime (CaO) – 5.2 % Potash (K 2 O) – 0.6 % Magnesia (MgO) – 3.6 % Alumina (Al 2 O 3 ) – 1.0 7

8. Types of Glass Obsidian is a natural form of glass that is created by volcanoes Soda-lime glass – The most basic, common, inexpensive glass – also the easiest to make – Used for manufacturing windows and bottle glass 8

9. Types of Glass (continued) Leaded glass – Contains lead oxide which makes it denser – Sparkles as light passes through it (light waves are bent) – Used for manufacturing fine glassware and art glass – Is commonly called crystal 9

10. Types of Glass (continued) Tempered glass – Stronger than ordinary glass – Strengthened by introducing stress through rapid heating and cooling of its surface – When broken, this glass does not shatter, but fragments or breaks into small squares – Used in the side and rear windows of automobiles 10

11. Types of Glass (continued) Laminated glass – Constructed by bonding two ordinary sheets of glass together with a plastic film – Also used by automobile manufactures 11

12. Glass as Evidence Class characteristics: physical and chemical properties Individual characteristics: if the fragments can fit together like pieces of a puzzle, the source can be considered unique

13. Considerations for Collection The collector must consider that fragments within a questioned sample may have multiple origins. If possible, the collector should attempt an initial separation based on physical properties. The collector must consider the possibility that there may be a physical match to a known sample (e.g., a piece of glass to a fractured vehicle headlamp). When an attempt to make a physical match is made at the site of collection, the collector should take precautions to avoid mixing of the known and questioned samples. Any glass samples collected should be documented, marked (if necessary), packaged, and labeled. —Forensic Science Communications

14. 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 Fractures Color Thickness Fluorescence Markings—striations, dimples, etc. Physical Characteristics

15. Forensic Science: Fundamentals & Investigations, Chapter 14 15 Density The formula for calculating density is: D = m / V The mass (m) of a fragment of glass can be found using a scale. Place the fragment of glass into a beaker filled with water and measure the volume (V) of overflow. Divide the mass (in grams) by the volume (in milliliters) to find the density (D) of the glass fragment.

16. Density Practice Find the density for the following pieces of glass: 1.Mass: 4g, Volume Displaced: 2mL 2 g/mL 2. Mass: 1g, Volume Displaced: 4mL.25 g/mL

17. Common Densities Type of GlassDensity window2.46–2.49 headlight2.47–2.63 Pyrex2.23–2.36 lead glass2.9–5.9 porcelain2.3–2.5

18. 18 Refractive Index When a beam of light moves from one medium into another, its speed changes. That change causes the beam to change direction, bend. Measure of how much the speed of light changes (n>1). (Air’s RI: n=1)

19. 19 Refractive Index The direction of the light forms two angles with the normal. If the light passes into a denser medium (the gray area), its direction will bend toward the normal.

20. Determination of Refractive Index Immersion method—lower fragments into liquids whose refractive index is different Match point—when the refractive index of the glass is equal to that of the liquid Becke line—a halo-like glow that appears around an object immersed in a liquid. It disappears when the refractive index of the liquid matches the refractive index of the object (the match point).

21. The Becke Line The Becke line is a “halo” used to determine refractive index. It can be seen on the inside of the glass on the left, indicating that the glass has a higher refractive index than the liquid medium. The Becke line as seen on the right is on the outside of the glass, indicating just the opposite.

22. Common Refractive Index LiquidRIGlassRI Water1.333Vitreous silica1.458 Olive oil1.467Headlight1.47–1.49 Glycerin1.473Window1.51–1.52 Castor oil1.482Bottle1.51–1.52 Clove oil1.543Optical1.52–1.53 Bromobenzene1.560Quartz1.544–1.553 Bromoform1.597Lead1.56–1.61 Cinnamon oil1.619Diamond2.419

23. Snell’s Law of Refraction Can figure out the RI of materials based on the angle the light hits and bends. n 1 sin(θ 1 ) = n 2 sin(θ 2 ) n 1 = RI of incident light θ 1 = angle of incident light n 2 = RI of refracted light θ 2 = angle of refracted light

24. Snell’s Law Example 1 Light traveling in air (n 1 =1) hits a piece of glass at an angle of 30 degrees. The light refracts in the glass at an angle of 15 degrees. What is the index of refraction (RI) of the glass? n 1 =1, θ 1 = 30, θ 2 = 15, n 2 =? 1sin(30)=n 2 sin(15) 0.5=0.2588n 2 n 2 = 1.93

25. Snell’s Law Example 2 Light traveling in air (n 1 =1) hits a piece of glass at an angle of 45 degrees. If the glass has a refractive index of 1.5, what angle should the light bend at? n 1 =1, θ 1 = 45, θ 2 = ?, n 2 =1.5 1sin(45)=1.5sin(θ 2 ) 0.7071=1.5sin(θ 2 ).4714= sin(θ 2 ) θ 2 = 27 degrees

26. Snell’s Law Practice 1. Light traveling in air (n 1 =1) hits a piece of glass at an angle of 37 degrees. The light refracts in the glass at an angle of 30 degrees. What is the index of refraction (RI) of the glass?