Forensic Analysis of Glass

A series of flashcards covering key concepts related to the forensic analysis of glass, including its composition, properties, types, breakage patterns, and evidence collection methods.

What is the basic composition of glass?

Glass is primarily composed of a fusion of sand (SiO2), soda (Na2CO3), and lime (CaO).

What are the primary physical properties of glass?

Glass is hard, elastic, brittle, a non-conductor of electricity, and has specific density and refractive index.

What is borosilicate glass and its purpose?

Borosilicate glass, like Pyrex, has 5% borax added to it to resist breaking when heated or cooled.

What type of glass is commonly used in doors and windows?

Flat glass is commonly used in doors and windows and is made by a 'float glass process'.

How does tempered safety glass differ from regular glass?

Tempered safety glass is designed to break into tiny pieces and has potassium replace sodium on the surface.

What types of cracks form when glass breaks due to an impact?

Radial cracks form first on the side opposite the force, followed by concentric cracks on the same side as the force.

What does the 3R rule in glass fracture analysis stand for?

Radial cracks give rib marks that make Right angles on the Reverse side from where the force was applied.

What is a notable exception to the Three R Rule?

Tempered glass 'dices' and does not form ridges, and small tightly held windows do not bend significantly.

What changes occur in cracks when a bullet impacts glass?

The load side is the entrance side, while the unloaded side is the exit side, with rib marks indicating break force.

How can examiners reconstruct broken glass evidence?

Examiners can fit together pieces of glass to determine they originated from the same object.

What should be done with glass fragments collected as evidence?

Glass fragments should be packaged in boxes to avoid further breakage, with whole items individually wrapped.

What are the goals of forensic examination of glass evidence?

To determine types of glass, how it fractured, classify it using physical characteristics, and individualize it to a source.

What types of properties are compared in glass forensic analysis?

Optical properties include color and refractive index, while non-optical properties include surface wear, striations, and density.

How are optical properties of glass analyzed?

Optical properties are analyzed through side-by-side comparisons using similar-sized fragments under various lighting.

What hardness level does glass generally have on the Mohs scale?

Glass has a hardness level of 5-6 on the Mohs scale.

What does surface striation analysis reveal about glass evidence?

Surface striations can indicate the glass's orientation and are useful for individualizing evidence.