Paints, Dyes and Pigments

Question 1

what is a dye

Answer 1

its soluble, organic based and used in textiles

Question 2

what is a pigment

Answer 2

its insoluble, organic and inorganic based and used in paints, plastics and glass

Question 3

Classifying colours

Answer 3

used the colour index scheme (CI) and assigned a generic name
gives the properties, companies that manufacture, trade names and chemical composition

Question 4

what is paint

Answer 4

a surface coating –> a suspension of pigments and additives in a binder
- chips, fragments and flakes = v. delicate
- do not refrigerate or freeze (could add moisture)

Question 5

analytical work flow for dyes, pigments and paints

Answer 5

–> after raman
- SEM EDX, XRF
- XRD
- pyrolysis (GC-MS) = destructive

Question 6

benefits of using Raman

Answer 6

rapid and non destructive
sensitive
high spatial resolution
little sample prep
‘green technique’

Question 7

Microspectrophotometry

Answer 7

for colour determination
gives precise characteristic colour described as a distribution of wavelength
can be combined with all other microscopic techniques

detects light interactions with different parts of the surface

Question 8

Automotive paint

Answer 8

most common form of paint evidence. has a min of 4 layers
clear coat
base coat
prime
E coat
pre treatment
substrate
body (all 1/10th mm thick combined)

Question 9

ways to sample automotive paint

Answer 9

1. cross section - flat cut
2. thin peels
3. wedge cut
4. stair step exposure (more probative)

Question 10

X ray fluorescence

Answer 10

absorption of radiation at one energy and reemission at a diff energy due to filling of an e- vacancy
gives unique readings for each element
non destructive
no sample prep needed

Question 11

SEM EDX vs XRF

Answer 11

SEM - fast, non destructive, sensitive to low concs
XRF - lower LoD, larger samples needed

Question 12

Briggs law

Answer 12

n x wavelength = 2 x d x sin theta
integer x wavelength = 2 x interplanar spacing x sin (angle between plane and beam)