Categories
4: Materials and Process Colour

What is Colour? Light and Pigments

  • Colour cannot stand alone (Wassily Kandinsky)
  • Colour deceives continuously (Josef Albers)
  • Colour is an illusion, but not an unfounded illusion (C L Hardin)
  • Colour is accidental and has nothing in common with the innermost essence of the thing (Naum Gabo and Anton Pevsner)

Key Questions in Design

  • Does ‘colour’ exist?
  • Why is colour so difficult to define?
  • Why is mixing and combining colours so unpredictable?

Physics of light

Light consists of waves of electromagnetic energy which travel at different wavelengths.

Colour is the range of wavelengths of the electromagnetic spectrum that are visible to the human eye. Many other animals can perceive more wavelengths than we can.

When light strikes a surface, certain wavelengths are absorbed and others are reflected by its pigments or colouring matter. Objects emit many coloured wavelengths across the whole light spectrum. This process gives the object its surface colour.

Although the spectrum of lightwaves exists along a continuum, there are peaks of sensitivity or human perception that appear to be ‘hardwired in’ but also individually and culturally variable.

Although pure white light is perceived as colourless, it actually contains all colours in the visible spectrum. When white light hits an object, it selectively blocks some colours and reflects others; only the reflected colours contribute to the viewer’s perception of colour.

In many cultures we distinguish separate bands of wavelengths. (is this universal?? eg some do not distinguish green and blue)

Optical colour: additive and subtractive processes

Wavelengths reaching our eye – optical colour – are a combination of:

  • Surface or local colour
  • Lighting conditions

Virtually all our visible colours can be produced by utilizing some combination of the three primary colours, either by additive or subtractive processes.

Additive Primary Colours
Additive processes create colour by adding light to a dark background. RGB primaries are projected light on screens and monitors. Devices which use these primary colours can produce the maximum range of colour.
Subtractive Primary Colours
Subtractive process CMYK: Cyan, Magenta, Yellow. Pure Black is also added. Reflected light from pigments in printing and painting.

Subtractive processes are more susceptible to changes in ambient light, because this light is what becomes selectively blocked to produce all their colours. This is why printed color processes require a specific type of ambient lighting in order to accurately depict colours.

Colour properties: Hue, Value  and Saturation

A colour can be defined in terms of its hue, its brilliance and its saturation.Visually describing a colour based on each of these terms can be highly subjective, however each can be more objectively illustrated by inspecting the light’s colour spectrum.

Value/tone

The brain responds first to tonal and value structure of an image because the simple light/dark signals passed by the rods reach the brain more quickly than colour from the cones.

The actual range of lightness and darkness differs between hues, and this can cause difficulties in matching the brilliance. Yellow can only vary between a medium tone and very light; there is no such thing as a dark pure yellow. Red becomes pink when very light, and so loses its main qualities. Blue, however, covers the full range.

Hue
Hue is the position of a colour on the colour spectrum (see above). A colour’s “hue” describes which wavelength appears to be most dominant. Naturally occurring colours are not just light at one wavelength, but actually contain a whole range of wavelengths (see pigments below).

Hues are conventionally represented in colour wheels that can be used to help mix and also combine colours.

Munsell Colour Wheel
Munsell colour wheel that provides for more accurate mixing of complementary colours. It combines 5 primaries Yellow, Red, Violet, Blue and Green, 5 secondaries and 10 tertiaries. This system was then used in 1931 by the CIE System (Commission Internationale de l’Eclairage)
019502e71377398fc5d47a14d4c808f019ef32aaa8
Colour Wheel that includes different tonal values and combinations

Saturation
Saturation is a variation in the purity of a colour. A highly saturated colour will contain a very narrow set of wavelengths and appear much more pronounced than a similar, but less saturated colour. As they become less saturated, they become more grey, less ‘colourful’, and dirtier. Colours become unsaturated when they are mixed with white, black, grey or their opposite colours on the colour circle. Including saturartion

Some colour wheels combine all three dimensions of hue, saturation and colour.
01997331f471845ab0f869ecef9206e15d4399dcdb

Dyes and pigments

Colours of objects in the real world are not pure colours, but objects will reflect and absorb a range of wavelengths.

  • Pigments are bits of powder suspended in a medium such as gum, oil or acrylic.
  • Dyes are colouring materials dissolved in a liquid solvent.
  • Lakes are pigments made from dyes.

Materials to be coloured absorb dyes but pigments lie on the surface.

This is significant in choosing and mixing paints and inks. The brightest colours are produced by mixing warm colours with warm colours, and cool with cool. Mixing warm with cool colours gives more muted and neutral tones as a greater range of wavelengths are reflected.

Development of Pigments

Earth colours: prehistoric

Early humans used earth pigments (coloured clays that are found as soft deposits) on the cave walls such as yellow earth (Ochre), red earth (Ochre) and white chalk. Carbon (Lamp) black was also used, collected from the soot of burning animal fats.

Brighter colours: Egyptians and Chinese

Pigments were produced on a larger scale by the Egyptians and the Chinese. Earth colours were cleaned and washed increasing their strength and purity. Vegetable dyes were also developed by the Egyptians, who discovered the ‘lake’ making process of producing pigment and the basis of this process is still used by Winsor & Newton today to produce Rose Madder Geniune.

Blues and greens: new pigments appeared from minerals such as Malachite and Azurite. Egyptian Blue was first produced around 3,000 BC – a blue glass made from sand and copper which was ground into a powder.

Reds: Cinnabar made from minerals was the first known bright red. In China, the brilliant red that came from Vermilion was developed 2,000 years before it was used by the Romans.

Tyrian Purple came to signify power and wealth and was used by both the Greeks and the Romans. It was complicated to make, cost a fortune and involved using the mucus from thousands of Murex snails.

White: The Greeks also manufactured white lead, the first fully opaque white – namely Flake White and Cremnitz White – which involved stacking lead strips in a confined space amongst vinegar and animal dung.

Renaissance


Burnt Siennas and Umbers: Italians roasted siennas and umbers to make deeper earth colours. Terre Verte (Green Earth) was the principle under-painting colour for flesh tones.Utltramarine: from the semi-precious stone lapis lazuli, found largely in Afghanistan. As the most expensive pigment in the world artists used it to paint The Madonna’s clothing as a way of reflecting her status and power.

Synthetic methods

The opening up of trade routes in the 18th century coupled with advances in technology and science allowed for greater experimentation.

Prussian Blue: In 1704, a German colour maker Diesbach created Prussian Blue by accident in his laboratory and this became the first chemically synthesized colour.

French Ultramarine: 1828 a low cost blue was created by Jean-Baptiste Guimet. The artificial pigment is chemically identical to genuine ultramarine but physically finer and has none of the impurities of the lapis rock.

Chromes: The isolation of new elements in the late 18th century also played a part in providing new colours. Deposits of chrome in the USA in 1820 eased the manufacture of Chrome Yellow, a highly opaque low cost colour available in a variety of hues.

Zinc: The isolation of Zinc gave rise to Zinc Oxide which was used as an artists’ white in preference to lead white as it was less hazardous and more permanent particularly in water colour. However it lacked opacity until 1834 when Winsor & Newton developed a method of heating the oxide to increase its opacity. This new type of Zinc Oxide was called Chinese White.

Alizarin is arguably the most important organic pigment of the 19th century. It was found as a colourant in the roots of the madder plant, but independent work in both Germany and Great Britain managed to duplicate it synthetically in the laboratory – the first time this had ever been achieved. This more affordable synthetic pigment provided a blue shade crimson of strong tinting strength and high transparency and was an immediate hit with artists.

Reduction in price:

The explosion of new pigments during the 19th century, the invention of the metal tube and the arrival of the railways all combined to accelerate this movement. Bright new colours in portable, stable tubes and a method of easy travelling around the country helped give rise to some of the world’s most beautiful paintings.

Sources:
See website: http://www.webexhibits.org/pigments/

Wikipedia: https://en.wikipedia.org/wiki/Pigment

Cambridge in Colour:  Colour Perception