PROPERTIES OF COLOURS.
As already indicated, certain colours give an impression of warmth, and others two stars in red and white paper respectively, and fixing one beside the other on a neutral ground. as indicated by Fig. 470.
By looking at the red star for a few minutes, then at the white one beside it, a green and white star will be seen. This is clue to the phenomenon known as " visual fatigue." In the example under consideration, those muscles of the retina which convey the red sensation to the brain are, as it were, exhausted by con stantly gazing at that colour, and refuse any longer to perform their function. As a consequence, the two remaining sets of retinal muscles, those giving rise to the green and blue-violet sensations, are alone in action, and on looking at flit white star it appears to be green. For, as is more fully explained in the section on Photo graphy in Colours, the sensation of white light is compounded of the three primary an impression of cold. Warm colours have the property of approaching the eye, whilst cold colours recede from it. Thus, if a figure is required to stand out from the background, it should be painted in warm colours, and the background kept cool in tone. Every tint, however complex, as it approaches to either of the two extremes, red or blue, obeys the same law. Again, colours possess varying intensities. The darkest or least intense colour is purple, whilst the brightest colour is yellow, its complementary. Although yellow is that
which appears brightest, it is not the most exciting colour. Red occupies this posi tion, and, as may be supposed, the comple mentary to red has the opposite effect, being the most soothing colour. It is also evident that colours which are comple mentary to each other have their contrasts increased, whereas those which are not complementary are subdued in contrast and lose their purity. The same rule applies to the blending of colour and absence of colour, black and white. If a black is to look deep, pure, and rich it should be opposed by red, yellow, cr orange ; if opposed by blue or green, it appears brownish. The knowledge of these simple facts is often acquired intui tively, but time is saved and confidence gained if the novice makes himself familiar with the rules stated above.
Indigo. Naples Yellow.—A not very perma nent colour ; useful for flesh tints. Yellow Och•e.—Used in painting fair hair, and sometimes for backgrounds. Orange. Ver milion. Rose Madder.—A good transpar ent colour suitable for delicate flesh tints. Aureolin. Viridian. Carmine. —Use f ul in flesh tints ; works well, but not perma nent. Terre Verte. Chinese White. The colours can be obtained in either cakes, pans, or tubes. Moist colours in pans are, perhaps, the most convenient. A japanned