The Dimensions of Colour
Basics of Light and Shade
Basics of Colour Vision
Additive Colour Mixing
Subtractive Colour Mixing
Colour Mixing in Paints
Hue
Lightness and Chroma
Brightness and Saturation
Principles of Colour
References
Contact
Links
Next CLV Workshops:
JANUARY 2009
Sydney & Brisbane
PART 6. COLOUR MIXING WITH PAINT
Figure 6.1.Mixing of two near complementary opaque pigments, Cadmium Red and Cobalt Green. If the mixing process was purely subtractive, the mixtures would pass along the blue line through black; if entirely partitive, they would move along the white line.
Artists using traditional paint mediums mix colours in three basic ways:
1. physically mixing paints
2. glazing with superimposed transparent paint layers
3. interspersing tiny patches of colour that mix optically when viewed from
a distance.
The first two methods are primarily subtractive processes, but with some important qualifications. The physical mixing of opaque paints is usually described as simply subtractive, and occasionally as largely partitive, but in reality both processes are important (Figure 6.1, 6.2). In such a mixture, a large amount of the light bounces off grains of both components before emerging. Each component therefore has the opportunity to influence the colour of this light, whose colour on emerging will be the result of subtractive mixture. However, some light will just bounce off grains of one or other component alone. Consequently, even if two paints are perfect complementaries, the mixture will still reflect considerable light because of the contribution of this last component, which is the reason why it is impossible to mix a dense black from opaque paints. With paints having perfect transparency the process would be purely subtractive. The partitive component is greatest when the grains are not enclosed in a medium, for example in pastel.
Figure 6.2. Physical mixing of artists' paints. Physical mixing of opaque paints involves significant components of partitive (averaging additive) as well as subtractive mixing. With transparent pigments the process is more purely subtractive.
In glazing (Figure 6.3), most light will pass through both layers, resulting in subtractive mixing, but to the extent to which the top layer is not perfectly transparent, a minority will bounce off the top layer. Thus for example red glazed over blue looks different to blue glazed over red.
Figure 6.3. Glazing of imperfectly transparent paints. Mixing of overlaid glazes is primarily subtractive, but a minor additive component is supplied by the upper layer.
Mixing of tiny interspersed colour areas (Figure 6.4) primarily involves partitive colour mixing. Partitive mixing, as we have seen, is essentially a kind of additive mixing in which the two components average out rather than add quantitatively. Thus an area of yellow and blue dots in the right proportion to make a neutral will look grey rather than white, because it reflects less light in total than a white surface, which reflects all wavelengths over its whole surface. If there is any overlapping of the component colours (as in halftone printing), significant subtractive mixing may also occur. Mixing of tiny interspersed colour areas includes the pointillist technique of separately applied dots of colour; but can also include other methods such as colour showing through a discontinuities in an overlying paint layer, or watercolour washes containing a granulating component.
