Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

forensic chemistry > lecture 5 - chemistry of colour > Flashcards

lecture 5 - chemistry of colour Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

what colours are the three colour cones in the human eye?

A

blue, green and red

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what happens to the three cones in the human eye when seeing white?

A

all cones are stimulated equally

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what happens to the three cones in the human eye when observing orange?

A

stimulation of only two cones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

where can you find the 3 colour cones in the human eye

A

the retina at the back of an eye

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what does the CIE system base colour on

A

the coloured cones in the human eye

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is the drawback of the CIE system?

A

colour can only be described with this system, not quantified - due to the fact not all colours are represented equally in the diagram

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what do we use the Munsell system for in forensics?

A

used for the quantification of the colour of soil - when its wet/dry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is hue?

A

the actual colour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is value (in the Munsell system)

A

how light or dark a colour is - vertical axis - ranges from black (0) through to white (10)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is chroma (in the Munsell system)

A

how strong or weak your colour is - horizontal axis - varies continuously and ranges from neutral at the centre to maximum saturation at the outer edge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

name the 5 primary colours used in the Munsell system

A

red, yellow, green, blue, and purple

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

when labelling using the Munsell system what’s the order we use?

A

hue, value, chroma

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what are dyes soluble in

A

the solvent they are contained in - it has an affinity for the substrate it is deposited on

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what are pigments

A

particles suspended in a solvent - with no affinity for the substrate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is opacity

A

the ability of your paint to stop the transmission of light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what do pigments produce that causes opacity

A

scattering of light - the greater the scattering of the light the greater the opacity of a paint

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

what is optimal scattering

A

ensuring the diameter of the pigments particles are half that of the wavelength of incident light that is directed at the pigment particles e.g. white pigment particles need to be around 200-400nm as that’s half the wavelength of incident light for white

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is the definition of paint

A

a liquid that oxidises in the air or a coloured powder in a glue-like medium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what are the 5 things that make up paint and why do we use them?

A
  1. water
  2. pigment - for colour and opacity
  3. binder - to help bind the pigment to the wall
  4. surfactant & antifoam - to reduce bubble
  5. thickener - thickens the paint once its on the wall
20
Q

to maximise scattering and reflection what 3 things do you need to ensure?

A
  1. pigment strength is high
  2. the pigment RI is higher than the binder RI
  3. the size of the pigments particles are half the wavelength of incident light
21
Q

give an example of an inorganic pigment

A

Titanium dioxide (TiO2)

22
Q

name the 3 crystal structure Titanium dioxide exists in

A

Rutile
Anatase
Brooktite

23
Q

which of the three crystal structures of Titanium dioxide is not used in the production of white paint

A

Brooktite

24
Q

which of the three crystal structures of Titanium dioxide produces the best opacity in white paint

A

Rutile as its RI is the greatest

25
Q

why is paint that contains Titanium dioxide photocatalytic (self cleaning)

A

sunlight will react with the TiO2 in the white paint and oxidise any dirt found in the paint

26
Q

what are luminescent pigments used in and how do they work

A

fluorescent inks and paints e.g. found in emergency exit signs. They work by absorbing light of a specific wavelength and emitting light of a longer wavelength

27
Q

what are pearlescent pigments used in and how do they work?

A

pearlescent paint used on cars. They work due to the differences in the RI of the pigment (high RI) and the mica (low RI)

28
Q

what are thermochromic pigments and how do they work?

A

pigments sensitive to temperature - they change colour when heated up or cooled down

29
Q

name 4 different dyes used in forensics (only one acid)

A
  1. solvent black
  2. gentian violet
  3. acid yellow/black/violet
  4. indigo
30
Q

name an example of an azo dye

A

solvent black

31
Q

what is solvent black used for in forensics?

A

the detection of oil based fingerprints

32
Q

Name a basic dye used in forensics

A

gentian violet

33
Q

what is gentian violet dye used for in forensics

A

the detection of oil based fingerprints on the adhesive side of tape

34
Q

Name the three acidic dyes used in forensics

A

acid black/ yellow/ violet

35
Q

what is acid black (and yellow & violet) used for in forensics

A

the detection of fingerprints in blood as they bind to the haem group of blood

36
Q

Name a carbonyl dye

A

indigo dye

37
Q

give a use of indigo dye

A

blue fibres - mostly found in jeans

38
Q

name the three less common dyes and their uses

A
  1. Methyl violet - the main dye found in ballpoint pen ink
  2. Basic red 40 - used to further enhance white superglue fumed fingerprints
  3. Copper phthalocyanines - used in pigment paint and the detection of fingerprints
39
Q

name the three types of pigments

A

inorganic (TiO2), organometallic (contain a transition metal complex), and natural (lapis lazuli)

40
Q

name the 3 general components found in ink

A
  1. Colourants - such as dyes and pigments
  2. Solvents - the vehicle for the colourant
  3. Additives
41
Q

what does the type of solvent used in inks depend on

A

the age of the pen - older inks used oil based solvents and newer inks use glycol based solvents

42
Q

name 3 additives to inks and what they are used for

A
  1. fatty acids - lubricate the ball in the pen
  2. natural resins/ synthetic polymers - help to dissolve your inks within the solvent to make the ink go further
  3. organic additives - prevent corroding
  4. glycols and Formamide - ensure a pen will not dry out
43
Q

name the three ways we analyse dyes in inks and what they do

A
  1. UV-Vis spectroscopy - helps us differentiate between inks
  2. IR spectroscopy - determines the composition of inks
  3. Raman spectroscopy - helps us differentiate between inks
44
Q

name the 4 ways we analyse dyes in fibre in forensics

A
  1. ATR-FTIR - non-destructive
  2. HPLC and TLC
  3. UV-VIS attached to a microscope - non-destructive
  4. UV-Visible spectroscopy and Raman spectroscopy - UV is only tentative whereas Raman is confirmatory
45
Q

name the three ways we analyse pigments in paint forensically

A
  1. Fourier transform infrared (FTIR)
  2. Raman and FTIR spectroscopy
  3. X-Ray fluorescence

forensic chemistry (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions