Color Bias of Artist Pigments
Every pigment has a color bias, meaning the color encroaches a neighboring hue on the color wheel. Even the purest primary colors will have a color bias as they can never possess the purity of scattered light. This color bias will affect how the pigment mixes with other pigments and how it looks when thinned with art mediums and applied as a glaze.
The Purity of Artist Colors
Cool Red Pigments for Art
The true primary colors are yellow, magenta and cyan (as can be seen with printing ink). In painting terms, cadmium yellow (pale), permanent rose and pthalo blue closely resemble these primary colors. But every pigment, regardless of how apparently pure, possess a color bias. This color bias will become obvious when a chosen pigment is applied as a thin glaze or mixed in with other colors. Warm Blues in Pigment
French ultramarine is frequently used for its depth of hue. But apply a thin glaze of this blue and it will appear slightly violet. This is because ultramarine blue is slightly biased towards red. Any blue containing red would not be a good blue counterpart with yellow to produce pure greens but would be the ideal counterpart to produce purple or mauve. So in this respect, ultramarine is a warm blue as it is slightly biased towards red. Other warm blues include Winsor blue (red shade), cobalt blue and Indanthrene blue.
Cool Blues in Pigment
By contrast, blues biased towards green are cool blues. Cool blues include cerulean blue, Winsor blue (green shade), pthalo blue, manganese blue, monestrial blue and turquoise. Such cool blues would be suitable for mixing pure greens, for they possess very little red, but would be unsuitable for mixing purple or mauve. Prussian blue is a brownish-blue as it contains quite a lot of color impurities. Warm Reds in Painting
Some reds are biased towards yellow, giving them a glowing or orange cast. Such warm reds include cadmium red, flesh tint, Winsor red, bright red and scarlet lake. Spread a thin film of any of these colors via artist spirits and their yellowish cast will become apparent. As they possess yellow, these reds would be an unsuitable counterpart with blue to produce a clean violet or purple, but would be ideal for mixing orange.
Some reds tilt slightly towards violet in their color bias and are therefore cooler than the reds just mentioned. Cool red pigments include permanent rose, carmine red, alizarin crimson, magenta, quinacridone and rose madder. As these reds contain a little blue, they may not produce clean, dazzling orange if mixed with a chosen yellow. Again, spread a thin glaze of these reds and their violet cast will become apparent. Yellow Hues Cool and Warm
Like blue and red just mentioned, yellow pigments also possess a color bias. Warm yellows (biased towards orange) include cadmium yellow, Indian yellow, cadmium yellow (deep) and Winsor yellow (deep). As these yellows are warm, any would be a suitable counterpart with red for mixing pure orange.
Cool yellows that are biased towards green can be found in lemon yellow, cadmium lemon and Bismuth yellow. Any of these yellows would be suitable for mixing clean, dazzling greens.
Impurities in Artist Pigments
Many popular artist pigments possess a lot of impurities, as they comprise a blend of all three primary colors. Earth colors such as Vandyke brown, yellow ochre and Paynes grey are such examples. But even these have a particular color bias. Burnt sienna tends to have an orange-red cast. Burnt umber has a violet-blue cast. Indian red and Venetian red have a violet-red cast. Some green pigments, again possess a lot of impurities, such as olive green and sap green. But clean greens can be found in viridian, Winsor green and chrome green.
Black pigments possess the most impurities of all, as all three primary colors in approximately equal measure are required to produce them. Spread a thin film of lamp black or ivory black and you will be surprised to find a rainbow of pigments, including yellow, violet and red.
Purity of Color in Art
In order to establish how pure a color is or in which direction it is biased, spread a thin film of this color as a glaze and surprising colors will appear to spread out before you. Even the purest colors possess a color bias. In the same way, impurities will become apparent when mixing a given color with another. A blue that possesses a violet bias, as in the case of ultramarine, will produce a muddy green when mixed with yellow. Some pigments give surprising results when blended with one another.
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