The French Post-Impressionist Georges-Pierre Seurat (1859-91) developed a system known as pointillism (also divisionism) whereby colour of different hue are placed side by side in line or dots. The principal idea is that when viewed at a distance, the colours are mixed "in the eye" i.e. optically, which also works best if the painting is viewed from a specific location for the best effect; to help see colours at their most intense the Art Institute of Chicago has placed a bench, approximately six feet away for optimal viewing: further away and the colours dissolve into neutrals.
The photographic image of Seurat's Un Dimanche après-midi à l´Île de la Grande Jatte A Sunday Afternoon on the Island of La Grande Jatte has been decomposed to show changes in hue. To alter the hue of the image is to colourise it. In a colour circle, white and black are starting and arrival points and are superimposed. They represent
- Red colour at the top of the circle.
- Grey intermediate levels correspond to intermediate hues on the colour circle.
- dark grey to orange.
- mid grey to green.
- light grey to magenta.
Specifically it is the difference in hue which is emphasised. The diagonal of the shore line is strongly differentiated by use of colour (change in hue). The diagonal line leads the viewer into the scene - Parisians enjoying an afternoon in a local park and then on through to infinity. Other details can be seen in his use of change in colour. Seurat has arranged the figures, and repeated similar groups of figures along the horizontal. Seurat's foreground figures and trees provide a vertical frame.
Light and Colour in Advertising and Merchandising
M. Luckiesh in "Light and Colour in Advertising and Merchandising" (1923) defines a pure colour as:
"a colour approaching the purity of spectral colours, that is the colours of the spectrum. For the sake of simplicity pure colours may be termed hues. The nearest approach to pure colours is obtained by some pigments and dyes. In fact many of the concentrated dyes may be considered dyes for most purposes."