How is the analysis of glass used in CSI?
Fragments of glass from headlights at a hit-and-run scene can leave clues about the unknown vehicle. Also, glass fragments can help police determine which direction the first bullet was fired through the glass. These clues can be gathered through the analysis of even the smallest fragments of glass.
How do you analyze glass evidence?
Forensic glass samples can be analyzed by comparing the refractive index of the sample to that of the possible source. Examination of samples under a regular microscope or a scanning electron microscope can give detailed information about the sample’s physical and chemical characteristics.
How can you determine the direction the glass was broken?
Determine the Direction of Force Find the sharply tapered pieces nearest to the hole (radial break pieces). Be sure you know which is the inside (or outside!) and look at the glass from the side. The force of the bullet hitting one side will break away a crater on the opposite side of the glass.
How you will analyze the density of glass samples?
The density of an unknown sample of glass is determined by placing a glass sample into suspension in a liquid solution. The density of that liquid is then either measured directly or used comparatively with another sample of glass.
What are the two most often used methods of glass analysis?
The projects focus on the two elemental analysis techniques X-Ray Fluorescence (XRF) and Laser Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) that are commonly used by forensic glass analysts.
How is glass collected at a crime scene?
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 are stress marks in glass?
Stress marks, seen on a cross section of a glass fracture, are shaped like arches that are perpendicular to one glass surface and curved nearly parallel to the opposite surface. The importance of stress marks stems from the observation that the perpendicular edge always faces the surface on which the crack originated.
What is the 4R rule for determining direction of force?
The ridges (Wallner lines) on radial cracks nearest the point of impact are at right angles to the side opposite, or to the rear, of the impact. This phenomenon is referred to as the 4R rule, (Ridges on Radial cracks are at Right angle to the Rear.)
What are the class characteristics of glass?
Hard, amorphous solid.
What is density test of glass?
One method is to measure the density of glass through the flotation method. In the flotation method a glass fragment will either float in a liquid of greater density, sink in a liquid of lower density, or remain suspended in a liquid of equal density.
What is glass density?
The density of glass is 2.5, which gives flat glass a mass of 2.5kg per m2 per mm of thickness, or 2500 kg per m3. Compressive strength. The compressive strength of glass is extremely high: 1000 N/mm2 = 1000 MPa.
What techniques do you use 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.