Monday, 11 October 2010

Why Does Red and Blue Make Grey?

Muddy colour mixes may appear from nowhere when trying to mix red and yellow for trees or blue and red for flowers. Grass’s green has a brownish cast; pansy heads look almost black rather than violet, and sunsets look tarnished. What can the artist do to avoid dirty mixes when combining primary colours?

Dirty Colours in Painting

How to Mix Clean Violets
Rachel Shirley
Understanding the causes of dirty colour mixes will help prevent dirty looking paintings in the future. The following bad practices will most certainly be the causes of unexpected colour mixes.
  • Not understanding colour theory properly.
  • Following a colour wheel diagram that does not display the true primary colours.
  • Using the mixture of any red, yellow or blue to mix green, purple or orange.
  • Having insufficient pigments in the artist’s arsenal to produce the desired colour mixes.
The Colour Wheel Chart Theory

Muddy colours often result when the artist mixes two colours that are not really primary colours. A true primary colour is one that cannot be made by the mixture of any other colour mix and is close to the purity of scattered light. Traditional art books purport these to be red, yellow and blue. But take the example of blue colours, of which there are many varieties, including:
  • Ultramarine blue
  • Cobalt blue
  • Prussian blue
  • Cerulean blue
  • Pthalo blue
  • Winsor blue
Just because an oil pigment is labelled “blue,” does not mean it is a primary colour. Ultramarine, for instance, has a lot of violet in it. Cerulean has a greenish tinge. In fact, no pigment is truly a primary colour, as impurities will exist, however small. Only a close approximation can be achieved. However, I have found Pthalo blue to be close to primary blue and include it in my colour palette.

See my Youtube clip explaining color theory

What is Primary Red?

Take the other counterpart in a purple mix, red, and here lies the same problem. Many pigments are considered “red,” including cadmium red, vermillion, crimson lake, alizarin crimson and permanent rose but not any “red” is a primary colour. Cadmium red has a lot of yellow in it and alizarin has a violet quality. Again, I have found permanent rose to be closest to a primary red, as it is similar to the “magenta” of printing ink.

How to Get Clean Purples

Since cadmium red is biased towards yellow and so is cerulean blue, the mixture of this “red” and “blue” will collectively have a lot yellow in it. It would really be like mixing red, yellow and blue rather than just red and blue. Small wonder if the mixture turns out brown or grey rather than purple. The same problem arises when mixing ultramarine, which has a violet cast, with cadmium yellow, which has an orange bias, to get green. The result turns out a brownish green.

What are the Primary Colours of Oil Paint?

Color Mixing Bible: All You'll Ever Need to Know about Mixing Pigments in Oil, Acrylic, Watercolor, Gouache, Soft Pastel, Pencil, and Ink
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I have found pthalo blue, permanent rose and cadmium yellow (pale) are pretty close to pure primary colours, although small impurities will still exist. Pthalo blue and lemon yellow will produce clean greens, although viridian will add a little punch. Pthalo blue and permanent rose will produce deep purples, although, substituting ultramarine for pthalo blue will result in warm purples (as it contains violet anyway).

So to avoid getting brown rather than purple, avoid using reds and blues that are biased towards yellow. The following pigments are either biased towards each other (ie have a violet cast in them) and will produce a variety of interesting purples, violets and mauves, or are almost a true primary colour.

Pthalo blue, Ultramarine, Winsor blue (red shade), Prussian blue, permanent rose, alizarin crimson and crimson lake. Quinacridone violet might add some punch.

Links to Advice on Colour Mixing

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