As opposed to projected, television and computer images, painters use the subtractive color principle. If a chemical that absorbs red and blue light rays is painted on to a surface, that surface will reflect what is left, the yellow rays ( it will appear to the viewer as yellow). If the surface absorbs red only, then it will reflect the other two and will appear green. If the surface absorbs all hues then it will reflect no colors and appear black. White is the sum of all hues while black is the absence of them. Different types of chemicals trap light rays of differing lengths when painted on surfaces.. If the chemical absorbs all red light and a little of the blue and a little of her yellow it will appear a darker green. If the chemical covered surface absorbs all the red light and only the red it will appear the green of the highest 'saturation'. The more light reflected of all types the higher the value. The more light absorbed the lower(darker) the value. This is the subtractive principle.
So would you expect a value five blue mixed in equal amounts with a value five yellow to produce a value five green? I must add here the chemical is to be considered non-transparent and if you squint hard at the colors below you will almost be able to see their 'value'.
■ The answer is not one (black), nor is it five, but that is the fault of the current indexing system and not your maths! The value will darken as a consequence of the subtractive
■ nature of the combined chemicals. All you need to realise is that mixing colors will not exactly average their combined values. A high value yellow mixed with a deep blue, say prussian blue, will produce a green slightly deeper than the mean or average.This can be
■ easily adjusted using black or white you may say; and so it can but you may lose some of the saturation you desire.
So you race out and buy a cadmium yellow medium instead of the cadmium yellow light you used! Now the value is correct, the saturation right but it is not the hue you had in mind. Another trip to the paint supplier?
This type of treadmill is to be avoided. Painters are great realists in matters of economy; they must be. Most know how to minimise outlays for maximum return. They learn quickly their color theory and know what suits them, and they tend to support it come what may. Often the introduction of a new color into their palette can approximate a birth in the family.
With white red blue and yellow all values are obtainable, thousands of hues and values are also available. Saturation is usually bought in small tubes and lasts forever. I advise, rather than buying black to mix it with your red, blue and yellow.
To make color your serf rather than you master you first subdue (use a limited palette), train (understand what makes the harmonies) and most of all get your values exact. All the great masters did as you see above in Vermeer's painting. (yellow ochre, light red, cobalt and cerulean).
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