THE ARTISTS' COLOUR WHEEL

What scale should we use to place our colours within the circle of hue? The oldest hue scale still in general use is the traditional artists' colour wheel, a symmetrical arrangement of three primary colours, yellow, red and blue, equally spaced at 120^o from each other, and opposite three secondary colours, violet, green and orange respectively. The term tertiary is sometimes used for six colours on the perimeter of the wheel between adjacent primary and secondary colours, and sometimes for neutralized colours mixed from all three primaries. Many artists know this wheel in the form presented by Johannes Itten:

Figure 7.2. Colour wheel arrangement as presented by Johannes Itten (from The Elements of Colour).

The artists' colour wheel has a fascinating pedigree. We've just seen that the step of representing hue in a continuous circle was first taken by Newton in his Optics of 1704. We also saw earlier that the origin of the system of red, yellow and blue primary colours is much older, dating back (alongside many other systems) to late Antiquity, but that the first visual representation showing secondary colours in relation to these is in a diagram in the Opticorum Libri Sex (1613) of Francois D'Aguilon (Figure 7.3) . D'Aguilon showed his "simple" colours white, yellow, red, blue, and black on a linear scale, and placed each of the three "composite" colours purple, green and gold ("aureus") in relation to the relevant pair of simple colours.

Figure 7.3. From François dAguilòn, Opticorum libri sex of 1613. Picture credit: Institute an Museum of the History of Science, Biblioteca Digitale

After Newton invented the circular dimension of hue, it was only a small step to apply this dimension to the artist's linear scale of "simple" and "composite" colours. This step seems to have been first taken in a diagram added to the 1708 edition of the Traite de la Peinture en Mignature, attributed to Claude Boutet (Figure 7.4). In this work the author took the additional step, thanks also to Newton's influence, of removing white and black from the scale of simple colours, leaving just yellow, red and blue as the three primary colours ("Couleurs Primitives"). In a move followed in most succeeding colour circles for artists, the author abandoned the unequal spacing of Newton's hue scale in favour of the equal spacing of the artist's colour scale. In the twelve colour version of the colour wheel on the right-hand side of Figure 7.4, this resulted in the three primary colours, yellow, red and blue, being evenly spaced at 0^o, 120^o and 240^o respectively, and each directly opposite one of the three secondary colours (purple, green and orange respectively). Notice that the clockwise sequence of colours follows the order of the artists' colour scale (yellow-red-blue) rather than the sequence of the spectrum (red-yellow-blue), so that the order of the colours around the circle is reversed compared to Newton's. The result is essentially identical to the colour wheel of Itten.

Boutet presented this circle alongside another one with seven colours which, unlike Newton's, are evenly spaced, and include two reds and no "indigo". This seven-hue circle shows the actual pigments from which the remaining colours were mixed (Lowengard, 2006: note that the "primary" red was actually mixed from scarlet and crimson!).

Figure 7.4 Hand-painted colour circles from the 1708 edition  of Traite de la Peinture in Mignature, attributed to Claude Boutet, including the oldest example of the symmetrical 12-hue artists colour wheel (right). Picture Credit: Kuehni (2003)

No doubt because of its appealing neatness and simplicity, the symmetrical twelve-hue system proved enduringly popular among artists, designers and teachers. In its original orientation, or rotated, it appears in numerous versions in the writings of later theorists and artists. Assisted partly by the inexplicable popularity of Itten's books, it remains for many the colour wheel.

When Boutet wrapped the artists' colour scale symmetrically around Newton's circle, each of the primary hues suddenly and automatically found itself in a relationship of opposition to one of the secondaries. The difficulty is that, as we have seen, there are three fundamentally different kinds of opposing or complementary relationships among hues, and the hues that oppose each other are somewhat different in each case:

1. Psychological complements: hues that are opposite experiences e.g. unique yellow and unique blue, unique red and unique green.
2. Additive complements: hues of lights that mix to make white light e.g. "Monitor Yellow" and "Monitor Blue" (deep violet-blue), "Monitor Red" and "Monitor Cyan", "Monitor Green" and "Monitor Magenta"..
3. Pigmentary complements: hues of artists pigments that mix to give black or grey, e.g. yellow and violet, scarlet and blue, crimson/"magenta" and green.

The complementary relationships embodied in the traditional artists' colour wheel are in part psychological (e.g. red opposite green) and in part pigmentary (e.g. yellow opposite violet). The artists colour wheel, like the artist's colour scale before it, embodies pigment mixing relationships, but with the subconscious assumption (in my opinion) that a place must be found for the four psychological primaries. Red and blue owe their status as traditional primaries to the fact that they are the psychological primaries closest to the ideal subtractive primaries magenta and cyan respectively. As we've just seen, red's status as a primary colour was not even disturbed by the fact that Boutet had to mix it from scarlet and crimson paint. Green was forced into position opposite its psychological complement red, even though pigment mixing experience (as well as the evidence of afterimages) would place cyan opposite unique red. The artist's colour wheel is a compromise, developed on the assumption that only a single colour wheel was needed, at a time when these different kinds of complementary relationships were not understood. Fatuous attempts to devise a single all-purpose "real colour wheel" persist down to our own time. In reality we need different hue circles to represent each set of relationships accurately (Figure 7.5). Which one we use depends on specifically what kind of question is being asked.

Figure 7-5. The three hue circles. The diagram shows hue circles based on (A) opponent relationships of the unique hues or "psychological" primaries, (B) additive complements, and (C) pigmentary complements.

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