Ideal black is total absence of light, and can only be realized as a sensation, in the presence of light, which may however be in contrast or in association.

The nearest approach to ideal black by contrast, is to view a hole in a box with a blackened interior, so arranged that no light entering the hole, can be reflected back to the vision: in this way associated light, if not entirely absent, is reduced to a minimum and total darkness is practically realized by the vision in contrast with the surrounding light.

Pigmentary black viewed under diffused daylight conditions is always associated with white light, as no substance, however black it may be, absorbs all the impinging light; as examples, the following measurements of three white and three black pigments were made at an angle of 45 degrees with a light intensity of 25 units.

This is a true quantitative analysis of the 25 units of white light after reflection from the black pigments. The black units represent the proportion of white light absorbed, whilst the beams reflected from the pigments consist of the colour values developed which are associated with the unabsorbed white light.

TABLE II.

Lime SulphateBlue BlackLamp BlackIvory WhiteZinc WhiteWhite Lead
Standard light units 25·0
Black units (light absorbed) 9·0 9·2 9·2 — ·08
Violet units (colour developed) 2·2 1·4 1·4 — —
Blue units (colour developed) 1·0 1·9 ·4 ·01 ·05
Green units (colour developed) — — — — ·07
Associated white light 12·8 12·5 14·0 24·99 24·80
Totals25·025·025·025·025·025·0

The analyses demonstrate that black is not itself an active energy analogous to colour, but is a minus quantity distinguishable by contrast with the original light. The reflected beam consists of the colour developed, associated with the residue of unaltered light.

Note.—Suitable proportions of Violet and Blue give character and value to black, whilst Orange and Yellow are less pleasing as tending to rustiness.