particulates week 3

Question 1

define glass

Answer 1

a transparent, non-crystalline, amorphous solid

Question 2

what is the main composition of glass

Answer 2

1. silica (sand)
2. soda ash(sodium carbonate)
3. limestone (calcium carbonate)

Question 3

what is the forensic relevance of silica(sand) being in glass

Answer 3

composition of the sand from rocks can have different elements

Question 4

what is the purpose of soda ash (sodium carbonate) in glass

Answer 4

lowers the temperature at which silica will melt

Question 5

what is the purpose of limestone in sand

Answer 5

it is a stabilizer, stops water and humidity dissolving glass (waterproofing)

Question 6

what are the two categories that glass is forensically split into by use

Answer 6

1. plate (windows)
2. moulded (ornaments etc)

Question 7

how does toughened glass break?

Answer 7

breaks into small cuboid type fragments

Question 8

how does plate/float glass break?

Answer 8

goes into shards and slivers of glass

Question 9

how does laminate glass break

Answer 9

goes into shards and slivers of glass, but will not break due to laminate (plastic either side)

Question 10

what are the 2 fractures that occur in glass when it breaks?

Answer 10

1. concentric
   2.radial

Question 11

what are concentric and radial fractures?

Answer 11

concentric: glass will go back in the direction force applied
radial: glass will go in direction of force applied

Question 12

what are the 3 fractures that can occur in glass

Answer 12

1. forking
2. hertzian cone
   3.chatter marks

Question 13

draw a forking analysis both low stress and high stress

Question 14

what is the hertzian cone?

Answer 14

the void in the glass produced as an object passes through

Question 15

what are chatter marks

Answer 15

generated by friction on the surface of the glass, generates distinctive surface curved stress line

Question 16

what are the two types of chatter marks+ draw them

Answer 16

1. conchoidal
2. hackle marks

Question 17

what are conchoidal lines?

Answer 17

microscopic stress fractures that radiate from the point of impact

Question 18

what are hackle marks?

Answer 18

stress lines radiating in a perpendicular direction from the conchoidal lines, facing away from impact

Question 19

what does the quantity of glass backward transfer depend on?

Answer 19

1. proximity to source (inverse square law)
2. force of impact/object being used
3. nature of glass source (toughened/laminated)

Question 20

what are the forensic opps of glass?

Answer 20

1. jigsaw fit
2. morphology (tint/colour/pattern matching etc)
3. refractive index
4. elemental composition

Question 21

what is refractive index?

Answer 21

the ratio of the speed of light in a vacuum compared to the speed of light in another substance

Question 22

what does n represent in the refractive index equation?

Answer 22

refractive index of the substance

Question 23

what are the two processes for analysis for glass RI?

Answer 23

1. Submersion
2. submersion + low power microscopy

Question 24

what does the submersion + low power microscopy involve?

Answer 24

1. submerge glass in liquid (Known RI)
2. view under low power microscope
3. if RI of liquid= different from glass the becke line will show

Question 25

what does it mean if the becke line is on the outside of the glass edges

Answer 25

the RI on liquid is higher then the glass

Question 26

what does it mean if the Becke line is on the inside of the glass edges

Answer 26

liquid has a lower RI then the glass

Question 27

how do you know if the liquid and the glass have the same RI?

Answer 27

The Becke line will disappear

Question 28

what is used for the chemical analysis of glass?

Answer 28

SEM-scanning electron microscopy