Soil-Glass-Paint Review

soil formation

physical and chemical weathering

physical weathering

temperature, water and wind that breakdown rock

chemical weathering

rock dissolves or changes through chemical processes (oxidation reactions, acidic rain)

soil composition - organic

humus- decayed plant and animals

soil composition - inorganic minerals

can glow in the presence of black light

soil texture

sand-largest of three, see individual grains of sand

silt- between sand and clay in size, feels smooth, cannot be seen with the naked eye

clay- smallest of three, hold large amounts of water, can be very hard

red and yellow soil

oxidized iron

gray or blue soil

soils are wet for much of the year

dark colors

high organic content (humus)

forensic significance of soil

- can be used to link a suspect to a crime scene is there are significant similarities

- can be used to help suggest the general vicinity of a crime scene, if local geology is variable

- soil is collected at various intervals within a 100 yard radius for comparison

window glass

(soda-lime glass)- glass bottles and windows

lead glass

crystal stemware- more dense and more sparkly

pyrex

can withstand wide range of temperatures- kitchen and lab glass

laminated

two or more panes bonded by a plastic middle layer to prevent injury- car windshields, entrance doors, aquariums and display cases

tempered

glass crumbles into small chunks instead of long jagged pieces to prevent injury- side and rear car windows, shower doors, and glass tables

bullet resistant

laminated and tempered glass- windows and cars

density

d = m/v
flotation method

refractive index

measure of light bending due to a change in velocity when traveling from one medium to another

becke line equal

match point

becke line halo inside

glass has a higher refractive index than liquid

becke line halo outside

liquid has higher refractive index

radial

formed first
opposite to the side of the impact
lines originating from point of impact and extending to the edge of the glass

concentric

formed second
same side of impact
series of partial circles, one inside the other, sharing the same center

4 R Rule

ridge lines of Radial fractures are at Right Angles to the Rear of impact

side of impact

larger opening of a crater-shaped hole is made when the projectile exits the glass

properties of glass

Heat Fractures vs Blunt Force (Bullet) Fractures
Color
Thickness
Fluorescence
Markings- striations, dimples

paint pigment

mixture of inorganic metal salts to impart color

film former

organic polymers that hold paint and protect surface

electrocoat primer

applied to steel body of a car for corrosion resistance, colors from black to grey

primer surface

applied to primer to smooth out imperfections and seams, highly pigmented

basecoat

actual color of vehicle

clearcoat

improves gloss, durability, appearance, no pigment

paint chip

contain all layers of paint, come off of surface

paint smear

top layer which has loosened owing to being wet or air oxidation

Pyrolysis Gas Chromatography

uses heat to dissemble molecules and separates based on size, does not identify the chemicals in the paint, destroys the sample

FTIR Spectroscopy

detects the presence of certain parts in a molecule, does not show colored chemicals, analyzes all layers at the same time

UV visible spectrophotometry

dissolves colored chemicals to measure absorption and reflection of UV light

color layer analysis

requires cross section of paint chip, no smears, thickness must be same, class test

solubility

multiple solvents to see if paint bubbles, flakes, changes color, or dissolves