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
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
