Colours Theory

As for The Theory of Colours, Goethe in 1810 completed what he considered his most ambitious scientific project. He claimed the importance of human perception in the knowledge of nature, going against the contemporary progresses in Newton's experimental physics and his chromatic theory. Let's explore more about colour theory science and role in art history. 

Colour perception is essential to our experience of the world around us.  The visible light spectrum is only a segment of the entire electromagnetic spectrum that the human eye can view. This range of wavelengths is called visible light. 

Different objects are different colours because they absorb some wavelengths of the visible light spectrum, while others bounce off. The color we perceive an object to be is precisely the colour it is not, that is the segment of the spectrum that is being reflected away. For example a banana absorbs all the wavelengths but the yellow, which hit our eyes and is processed by our brain.

Light

Isaac Newton in 1666 used a prism to bend white light revealing its constituent wavelengths. This was something that had already been done before but this time he went a step further using another prism to put the wavelength back together again, changing the way we think about color forever. Until then it was unthinkable that white light could be broken down, instead it was supposed that the impurities in the glass created the spectral colors.

As for painting it is a different story. While mixing coloured light you get white, mixing many colour paints you get closer to black. The explanation lies in the science of optics. There are two different types of color mixing: additive and subtractive. Additive color mixing  happens when we mix lights of different colors, this is what Newton proved with his prism, the different light wavelengths are combined to create different colours, and when added together the result is white light, whereas subtractive color mixing occurs when we mix paints. Each pigment reflects back to the eye just a segment of the visible spectrum, when many are mixed together more and more wavelengths are subtracted, so we will perceive a black pigment or very close to it.

For painters this could be a problem. To keep a good quality of luminosity in the painting it is always better to use a single pigment rather than a mixture that will absorb more of the available light wavelength. In the history of art the search for more and brighter colours had been fundamental, from pre-history until today.

Paint

Pliny the Elder, a Roman author, in the first century AD wrote that painters in classical Greece used only four colors: black, white, red and yellow. We don't know if that's true since Egyptians by heating lime, sand and copper into calcium copper silicate, discovered the royal-turquoise pigment Egyptian blue at least as early as 2500 BC. But it is acknowledged that early artists were mostly confined to a small range of pigments they could extract from plants, insects and the ground.

Pigments had been discovered, traded and synthesised throughout recorded history, but with the Industrial Revolution the process accelerated dramatically in the nineteenth century. 

The availability of some pigments shaped the history of art. Paintings of Renaissance artists had a broader range of pigments compared to the prehistoric cave murals and the Medieval paintings and manuscripts. From that time some works remain unfinished because the artist couldn't afford the expensive pigments needed to complete the canvas. For example the clear blue ultramarine had to be bought by the commissioner, that often wrote in written contracts how much of the expensive paints they expected artists to use in the finished work, to avoid that painters would use a cheaper alternative. 

Artists had to work out their compositions to create reliable pigments, which were made by hand or some could also be obtained from specialists. 

In the late nineteenth century artists could really benefit from a ready-made pigments production, also with the invention of collapsible metal paint tubes in 1841. The new colors allowed artists to work with the brightest pigments anyone had ever seen. 

Colour Wheel

In the RYB colour model the typical pigment colour wheel includes primary, secondary and tertiary colours. The primary are the blue, red, and yellow.    Green, orange, and violet or purple are the secondary, created by mixing two primary colours. The tertiary colors,  green-yellow, yellow-orange, orange-red, red-violet/purple, purple/violet-blue and blue-green are then created by mixing primary and secondary colours.

Classification of pigments
Color_diagram_Charles_Hayter_edited.jpg
Moses_Harris_The_Natural_System_of_Colou

References:

The Theory of Colours, JW Goethe 1810

The Secret Lives of Colour, Kassia St Clair 2016