Chemistry of Colour

Question 1

How many colour cones do we have and what colours are they?

Answer 1

1. Red
2. Blue
3. Green

Question 2

How do we perceive colour?

Answer 2

• When we see the colour white all our are cones are stimulated equally.
• If you see a mix colour, only two cones will be stimulated.
• One cone can be more stimulated compared to another cone.

Question 3

What electromagnetic range can humans see colour?

Answer 3

380-700nm

Question 4

What does CIE mean?

Answer 4

Commission Internationale de L’Eclariage

Question 5

What are the roles of receptor cells in colour?

Answer 5

• The receptor cells are located in the retina and they can be divided into cone and rod cells.
• The rod cells are responsible for night vision so they have a low affinity for light intensity.
• Cones cells are used for colour sensing and they have a high affinity for light intensity.

Question 6

What are the tristimulus values for our coloured cones?

Answer 6

Blue= X
Green= Y
Red= Z
All equal values produce the colour white and this is due to all of our cones being stimulated.
The coordinates produce colours on the spectrum and some cones may be stimulated more than others.

Question 7

What is a drawback of the CIE system?

Answer 7

• It can describe colour but it can not quantify colour as it is not represented equally on the diagram.
• Does not distinguish light and darkness of colour.

Question 8

What can the tristimulus values be represented as?

Answer 8

• The values can be converted into two coordinates which can be located on the X and Y axis.
• The diagram they are plotted on is called a chromaticity diagram.

Question 9

What is the shape of the chromaticity diagram called?

Answer 9

Hyper parabola shape

Question 10

What is the relationship between the chromaticity diagram and saturation?

Answer 10

• The more saturated a colour is the closer to the edge of the parabola it will be.
• The more saturated a colour is means the more intense the colour is.
• Saturation is the strength of the dominant wavelength or hue.

Question 11

What is the difference between the Munsell system and the chromaticity diagram.

Answer 11

• The Munsell system describes and quantifies colour.
• The chromaticity diagram just describes colour.

Question 12

What is the Munsell system?

Answer 12

• It is a system that can describe and quantify colour.
• Can help in describing the colour of soil in forensics.
• Has three variables which are the Hue, Chroma and Value.

Question 13

Define chroma

Answer 13

The actual colour

Question 14

Define hue

Answer 14

How strong or weak a colour can be for example there could be two colours of blue that are different to one another as one can be described as ‘dark blue’ and another one described as ‘light blue’.

Question 15

Define value

Answer 15

• How light or dark a colour is.
• The depth of colour.

Question 16

What are colorants?

Answer 16

• They are chromophores (particles that absorb light).
• They impart colour to an object.
• Dyes and pigments are the main colorants.

Question 17

Describe the differences between dyes and pigments.

Answer 17

-Dyes are soluble in the solvent as they have a high affinity for the substrate it is deposited on.
-The pigment particles are suspended in the solvent and it is insoluble as the particles have not affinity for the solvent. Will not penetrate the solvent and will form a layer on the top of the surface.

Question 18

Define dyes

Answer 18

• They can be natural or synthetic, organic, inorganic.
• It is soluble and it has a high affinity for its solvent.

Question 19

What are the five types of dyes and what are they used for?

Answer 19

1. Acid- used for the detection of fingerprints.
2. Basic- used for the detection of greases or latent fingerprints.
3. Azo- product of fast BB test.
4. Natural
5. Direct

Question 20

What are the three types of pigments?

Answer 20

1. Natural
2. Inorganic
3. Organometallic- contains a transition metal that is surrounded by organic molecules.

Question 21

What does high and low opacity mean?

Answer 21

High opacity is when applying pain to a surface and not seeing the background colour and low opacity is applying a later of paint and seeing the background colour.

Question 22

What does transparent mean?

Answer 22

Light being allowed to be past through so objects can be seen distinctly seen.