CHAPTER XVI.
Contrast Colours—Measurement of Contrast Colours—Fatigue of the Eye—After-Images.
Fig. 45.—Method of showing Contrast Colours.
There is a phenomenon in colour which must be alluded to, and which possesses more than a passing interest to the art world, and that is colour contrast. Perhaps one of the best methods of showing this is by our colour patch apparatus. If we throw the reflected beam and the colour patch on a square as before, and place a rather thinner rod in front, so that the two shadows lie on a background of the combined white light and spectral colours, on passing a slit through the spectrum, the shadow which is illuminated by white light will appear anything but white. Thus if we allow yellow spectral light to illuminate one shadow, the other will appear decidedly of a blue hue; if a green ray it will be of a ruddy hue; if a blue ray of a yellow hue; that is, all the contrast hues will appear to the eye to tend towards a complementary tone to the spectral light. The kind of white light illuminating the shadow has a marked effect on the tone, as might be expected. The following table shows the contrast colour of the white illuminated shadow when the white light used was that of a candle.
| Spectrum Colour. | Contrast Colours in Electric light. | Spectrum Colour. | Contrast Colours in Gaslight. |
| Cherry red | Green gray | Cherry red | Green gray |
| Scarlet | Bluish green gray | Scarlet | Sap green |
| Terra-cotta | Blue gray | Light red | Green gray |
| Raw sienna | Light blue gray | Olive green | Pink gray |
| Olive green | Umber | Apple green | Mauve & black |
| Emerald green | Pinkish lavender | Emerald green | Pink terra-cotta |
| Grass green | Light pink | Emerald green | Pink terra-cotta |
| Bluish green | Dark pink | Bluish green | Pinker terra-cotta |
| Signal green | Salmon | Peacock blue | Salmon |
| Cyanine blue | Yellow ochre | Prussian blue | Reddish yellow |
| Ultramarine | Raw sienna | Ultramarine | Raw sienna |
| Violet blue | Brownish yellow | Violet blue | Brownish orange |
| Blue violet | Green yellow brown | Blue violet | Brownish yellow |
| Violet | Burnt sienna | Violet | Yellow ochre |
The contrasts here shown are not so visible when the two shadows of the rod occupy the whole of the white square, but are decidedly increased by the shadows occupying only a part of the field, the margins being illuminated with a mixture of the two lights. Not only are there contrasts with coloured light and white, but the relative position of one colour to another may alter the hue of each to the eye. The following experiments indicate what change can be expected in contrasted colours. The double colour apparatus was used as described at page 122, and a slit was placed in four different positions in the spectrum, viz. in the red, orange, green, and violet, to form patches, and another slit was placed in the same four positions in the other spectrum, and the contrasts noted.
| Original Colours. | Change due to Contrast. | ||
| Red | Orange | Red became yellower | Orange became green grey |
| Red | Green | Red unaltered, but brighter | Green unaltered, but brighter |
| Red | Blue | Red became more orange | Blue became greener |
| Red | Violet | Red became orange | Violet, no marked change |
| Green | Orange | Green became bluer | Orange became yellower |
| Green | Blue | Green became olive | Blue became more violet |
| Green | Violet | Green became yellower | Violet became bluer |
| Orange | Blue | Orange became redder | Blue became bluer |
| Orange | Violet | Orange became greener | Violet became bluer |
| Violet | Blue | Hardly altered | Hardly altered |
These contrasts were in most cases very marked, as would be seen by causing the same colours to fall on a different part of the screen, outside that on which the comparisons were made.