Forensic Examination of Glass Flashcards
1
Q
What are the levels of the analyze of a glass sample?
A
- preliminary examination
- measurements
- physical match
- physical properties
- elemental analysis
2
Q
What goes into Preliminary Examinations?
A
- note shape (flat, cylindrical, spherical)
- note surface texture and markings
note nature of fracture (fracture ridges, wavy thermal fractures, dicing) - note color (under both room light and UV)
3
Q
What goes into Measurements?
A
- thickness
- curvature
4
Q
What qualifies as a Physical match?
A
- usually worthwhile if the smaller of the two samples contains large glass flakes (1/4 in in diameter or larger)
- if this is successful no further examinations are needed
- pain, putty, rust stains and scratches may aid in physical matching
- ream marks may be used
5
Q
What are some Physical Properties of Glass?
A
- density
- R.I.
- Dispersion
- Color
- Hardness
6
Q
How is Density determined when examining glass?
A
- bouyancy
- flotation
density gradient tube - sink-float method
7
Q
How is Density determined when examining glass?
A
- buoyancy
- flotation
density gradient tube - sink-float method
8
Q
How is R.I. determined when examining glass?
A
- becke line, hot-stage
9
Q
Why measure Density of Glass?
A
- can be used as a screening technique with large numbers of fragments
- useful in identifying multiple sources present in the known and/or questioned samples
- it is nondestructive and an intensive property (not dependant on sample mass)
- need to measure very precisely in parts per hundred or thousand or better
10
Q
What is Displacement?
A
- a way to measure density
- directly determining mass and volume
- comparison by flotation
- comparison using a density gradient column
11
Q
What is the Gradient Column Method?
A
- Fragments of different densities settle at different levels in the column of liquid of varying density
- technique is not accurate for fragments that are cracked or contain an inclusion
12
Q
Explain the Density by the Flotation Method?
A
- glass particle is immersed in a liquid
- density of liquid is adjusted by the addition of small amounts of another liquid untill glass chip remains suspended
- when suspended, glass will have the same density as the liquid medium and can be compared to other relevant pieces of glass which will remain suspended, sink, or float
13
Q
What is R.I.?
A
- the ratio of the velocity of light in a vacuum to the velocity of light in any other medium
- an intensive property but it can be measured very precisely (0.0002) & does not destroy the sample
- R.I. of glass varies with small changes in composition or by ow it is manufactured
14
Q
What goes in Elemental Analysis?
A
- atomic absorption
- atomic emission (ICP-AES)
- Mass Spectrometry (ICP-MS)
15
Q
What are the Match Criteria?
A
- range test
- confidence interval
- student’s t test or Welch’s test
