Refractive index is the most commonly measured property in the forensic examination of glass fragments (Koons et al. 2002), because: Precise refractive indices can be measured rapidly on the small fragments typically found in casework.
What are the method used for matching of glass evidence?
(g/cm3 (solids); g/mL (liquids)) • One method of matching glass fragments is by a density comparison. Each type of glass has a density that is specific to that glass. If two samples of glass can be differentiated by density, they could not have originated from the same source.
What methods are used to identify glass?
The flotation and immersion methods are best used to determine a glass fragment’s density and refractive index, respectively. The latter involves immersing a glass particle in a liquid medium whose refractive index is verified unit it is equal to that of glass particle.
What are 3 ways that we can compare a piece of glass from the crime scene with a piece of glass from a suspect?
Glass examiners compare samples of glass found on suspects or found at the scene of a crime with a suspected source of known origin by measuring the physical and optical properties of color, thickness, density, and refractive index.
What is the only way to individualize glass?
What is the only way to individualize glass fragments found at a crime scene to a single source? The only way to individualize glass fragments is to piece them together like a jigsaw puzzle.
What is the 3R rule for glass fractures?
What is the 3R rule and how is it applied to the analysis of glass fractures? The 3R rule states that Radial cracks form a Right angle on the Reverse side of the force. This rule enables an examiner to determine readily the side on which a window or pane of glass was broken.
What are the 4 types of glass?
There are four main types or strengths of glass:
- 1) Annealed Glass. Annealed glass is a basic product formed from the annealing stage of the float process. …
- 2) Heat Strengthened Glass. Heat Strengthened Glass is semi tempered or semi toughened glass. …
- 3) Tempered or Toughened Glass. …
- 4) Laminated Glass.
What are the 2 types of glass fractures cracks?
When a projectile i.e. a bullet or rock hits the glass, it will form two distinct types of fractures: Radial and Concentric. There is another terminology that is known as cone fracture, observed to be caused by a penetration of the high velocity projectile such as a bullet.
What is a normal line in glass?
The perpendicular line that forms at the interface of two media is called the normal line. In this figure, as the beam of light moves from the air into the glass, the light slows down and bends toward the normal line.
What are two characteristics used to identify glass?
Glass: Glass can yield valuable information through fracture marks, lines and patterns. Testing for unique characteristics such as color, optical properties and density can determine the type of glass, for example a window pane, vase or glass bottle.
Why is it important for investigators to distinguish between different types of glass?
Trace evidence can be found at a crime scene in a number of different forms, including hairs and fibers, glass, or soil. Glass analysis includes determining the type of glass based on glass fragments. … The presence of the different materials in the glass makes it easier to distinguish one sample from another.
What is the elasticity of glass?
Glass is a perfectly elastic material: it does not exhibit permanent deformation, until breakage. However it is fragile, and will break without warning if subjected to excessive stress.
Where is glass evidence stored?
The glass should be placed in a sealed paper bindle or a folded and sealed paper or plastic bag, depending on size. Large pieces of glass with sharp edges should be put into sealed containers (such as cardboard boxes) in which they will not cut their way through. GLASS CONTAINERS.
Why is glass considered Class evidence?
Glass can be found as individual characteristic in cases where significant fitting of two glass fragments. … It is class evidence most of the time because without two fitting glass fragments, the glass can be identified but not linked to a specific object.