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Trace Evidence: Intro to Glass

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At a crime scene, glass that has been broken or fragmented is critical forensic evidence. Glass pieces from headlights may leave evidence about the unknown car at a hit-and-run crime scene. Investigators can also use window fragments or glass fractures to assess the direction, angle, and first cont...

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  • July 17, 2023
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  • 2018/2019
  • Lecture notes
  • Dave dibbs
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Trace Evidence: Introduction to Glass

Definition of Glass:
“An inorganic product of fusion that has cooled to a rigid condition without”
crystallization.
Glass Composition:
 Sand: Main component of glass, Primary former SiO2 (74%)
 Soda Ash: Low melting point, NaCO3 (16%)
 Limestone: Helps with insolubility in water, CaO (14%)
 Cullet: Scrappy of waste glass


 Sodalime glass accounts for majority of manufactured glass globally.
 The impurities in these main products can be used by the forensic
experts to discriminate glass of the same types. E.g. Burglaries


Types of glass:
 Flat Glass
 Float Glass
 Laminated Glass
 Toughened Glass
( glass breaks upon tension and not compression)




Flat Glass:

,  Uses float process and is the most common glass used
 Manufactured in flat sheets, comes in rolled and sheet forms
 Used in windows, doors and tables
How it's made:
Sand and other mixtures are made into a liquid which form the solid sheet
of glass.
Thickness is determined by spreading out the glass using liquid tin, it then
hardens. The tin remains a liquid because of it hardening point is lower
than that of glass.
The glass is the cut by scoring which then weakens the glass along a
particular line. This maybe used by machinery, however can be done
manually for made to order products.


Laminated Glass:
 A composite typically of a sheet of plastic between two sheet of flat
glass and is mostly used in Modern Windscreens
 Laminated glass are noted for their ability to act as a security glass,
also used in vehicles during collisions for passenger restriction


Toughened Glass:
 Also known as Tempered glass
 When broken it breaks into dices with no sharp edges
 It absorbs impact well used in mobiles and vehicles
 Achieved by rapid cooling of heated glass using air jets, this
compresses the surfaces and places the center in tension


Types of Fractures:
1. Low velocity fractures


2

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