glass and soil

Question 1

is glass evidence class evidence? can it be individualized?

Answer 1

yes, glass evidence is class evidence (from various sources). glass evidence can be individualized when a fracture match is found (from a specific source)

Question 2

what are characteristics of glass?

Answer 2

-amorphous solid: no ordered structure
-pure form made up of silicon and oxygen molecules
-high melting point (over 20,000° C)
-hard/brittle like a solid

Question 3

what are the different types of glass? can you give an example of each?

Answer 3

1. float glass/soda lime glass: windows
2. tempered glass: shower doors
3. borosilicate glass: lab glassware
4. tinted glass: car tinted windows
5. leaded glass (crystal): wine glasses

Question 4

how is sequencing of fracture performed? what is looked at?

Answer 4

fracture lines= radial and concentric
-radial fracture lines occur first extending outward from the break point
-concentric fracture lines form a circle about the break point
-radial lines always end in existing radial lines

Question 5

how is the direction of force of a bullet through glass determined?

Answer 5

direction of force= small projectiles-entry and exit holes
-entry= smaller hole, smooth surface
-exit= wider hole, crater shape, rough shape

Question 6

what are the class characteristics of glass that can be analyzed by most labs?

Answer 6

-physical appearance (size, shape, thickness)
-color
-density
-refractive index (RI)

Question 7

what is refractive index and is it useful for glass analysis?

Answer 7

refractive index (RI): the ratio of the velocity of light in a vacuum to its velocity in a medium
-refractive index determination can determine RI of small glass fragments using commercially available liquids

Question 8

is soil evidence class evidence? can it be individualized?

Answer 8

-soil evidence is always class evidence and has no unique qualities that allow for its individualization

Question 9

what are the characteristics of soil?

Answer 9

-consists of crushed rocks and minerals mixed with decayed plant and animal material (humus)
-varies in chemical and physical properties from place to place
-may be characterized by their color (color due to mineral and moisture constant using a Munsell Color Chart)
-some labs use high-performance liquid chromatography to separate and display humus components of soils