Glass as Evidence Properties The composition of glass

Glass as Evidence

Properties The composition of glass is unique and therefore identifiable. • What are some CLASS characteristic of glass

Physical vs. Chemical Properties • chemical composition (Si. O 2) • density (Physical) • refractive index (Physical)

Physical vs. Chemical Properties • The bending of light waves because of a change in velocity is called refraction.

How to find the Refractive Index Submersion method—used when glass fragments found at the crime scene are small Forensic Science: Fundamentals & Investigations, Chapter 14 5

Refractive Index • Place the glass fragment into different liquids of known refractive indexes • The glass fragment will seem to disappear when placed in a liquid of the same refractive index Forensic Science: Fundamentals & Investigations, Chapter 14 6

Video • http: //forensicsglassevidence. weebly. com/video. html

• Becke Line a halo-like effect appearing at the edges of a glass fragment Glass has higher refractive index-note white line inside • Glass has lower refractive index-note white line outside

What is Glass? • Glass is an amorphous solid. • Silica’s chemical name is silicon dioxide Would this structure affect HOW glass breaks?

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Types of Glass Safety Glass

What type of glass is this?

How is glass used by Forensic Scientist?

Glass as evidence • • • By analyzing the fracture patterns: 1. what object hit the glass 2. from which direction the object came 3. sequence of events 4. composition of specialized glass

CLASS or INDIVIDUAL EVIDENCE ?

Glass is Class Unless…. Glass evidence is considered class evidence, because it is mass-produced However if pieces of broken glass fit…

Slo mo glass • https: //www. youtube. com/watch? v=k. XNA 6 z. Af 8 uw&list=PLxz. BK 3 jp 20 D 46 KGEXZ 1 K 7 z. Jp. FGMLt. Ylrk&index=1

What pressure is found on ENTRY and EXIT side of glass?

Compression and Tension

ROT • Radial-----Opposite side----Tension

CSC • Compression---Same side---Concentric •

Primary Stops Secondary Forensic Science: Fundamentals & Investigations, Chapter 14 22

Path of a Bullet Passing through Window Glass perpendicular to the glass shot from the left shot from the right • The angles at which bullets enter window glass help locate the position of the shooter • Bits of the glass can fly backward (backscatter), creating trace evidence Forensic Science: Fundamentals & Investigations, Chapter 14 23

Entry and Exit holes

Handling of Crime Scene Glass Samples 1. Photograph glass samples before moving them. 2. Collect the largest fragments 3. Identify the outside and inside surface of any glass. 4. Sketch. 5. Note trace evidence such as skin, hair, blood, or fibers. 6. Package all materials collected to maintain the chain of custody. Forensic Science: Fundamentals & Investigations, Chapter 14 26

https: //www. youtube. com/watch? v=Whjma 0 lr. SXs Forensic files-shattered dreams