What must a forensic scientist evaluate when examining glass fragments?


When glass breaks what kind of cracks does it create?

Brittle materials like glass can’t bend, and so they break more easily. Researchers have traditionally thought that cracks in brittle materials grow because applied stress causes atomic bonds to stretch and pull apart at the tip of the crack. This process would produce sharp crack tips and smooth fracture surfaces.

Are cracks similar in plain glass and tempered glass?

Plain glass will yield true radial and concentric fractures which are similar to the sketch above. Tempered glass is designed to crack in such as way as when broken apart each broken piece of glass will be basically round with few pointed edges.

Are the first to form when a projectile passes through glass?

(T/F) A non-bullet projectile passing through a pane of glass will always cause the glass to shatter. (T/F) When an object begins to penetrate a pane of glass, concentric fractures are the first to form.

Which side of the glass will have the largest hole in glass fractured by a projectile?

“Bullet holes through thick glass will also form a crater, with (as is usually the case in bodies) the larger hole on the side that the bullet exited, and the smaller hole on the side it entered.

When a bullet passes through a piece of glass a distinct pattern is formed by the 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.

When a glass is broken radial cracks form a right angle on the reverse side of the force?

Concentric fracture- A crack in a glass that forms a rough circle around the point of impact. By analysing the radial and concentric fracture pattern in glass, the forensic scientist can determine the direction of impact by applying the 3R rule: Radial cracks form a Right angle on he Reverse side of the force.

Is glass individual or class evidence?

Glass can be found as individual characteristic in cases where significant fitting of two glass fragments. However, glass is usually class evidence therefore the value of evidence will depend on the discrimination powers of techniques used for its comparison.

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.

How is glass analysis used in forensic science?

A forensic glass analysis is typically a comparison of two or more glass fragments in an attempt to determine if they originated from different sources. Less frequently, it is a question of determination of end use, or glass provenance. The aim of a comparative glass analysis is to exclude possible sources.

How are glass fragments collected at crime scenes?

Place small glass fragments in paper bindles, then in coin envelopes, pill boxes, or film cans which can be marked and completely sealed. Place large glass fragments in boxes. Separate individual pieces with cotton or tissue to prevent breakage and damaged edges during shipment. Seal and mark the box containing them.

What must a forensic scientist evaluate when examining glass fragments?

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. In most cases, these have been good methods for differentiation between glasses.