Reflected Colour Is Never Pure: Yellow and Blue Make Green
How reflected lights mingle on a white sphere and rarely match the body they strike
This page of Melzi's fair copy of Leonardo's Treatise on Painting argues that no reflected colour is simple: light bouncing onto a surface mixes with all the other reflected colours meeting at the same place. A worked example has a yellow reflection a striking the part c o e of a sphere while a blue reflection b strikes the same spot, so that their mixture tinges a white sphere green, since yellow and blue mixed make a beautiful green. A second chapter states that reflections very rarely carry the true colour of the body where they meet, illustrated by a yellow sphere d f g e receiving a blue object b c and turning green. A third chapter begins to treat where a reflection is most visible, and two small pen diagrams of reflecting spheres accompany the text.
On this page
No reflected colour keeps its own hue alone
A colour reflected onto another body's surface never tints it purely with its own hue; it blends with every other reflected colour arriving at the same place. For the painter this means reflections must be rendered as mixtures, not as single clean colours.
Yellow a and blue b combine to green on the sphere c o e
The yellow colour a reflects onto the sphere at c o e, and the blue colour b reflects onto the same spot. Their mixed impact tinges a white sphere green, since yellow and blue mixed together compose a most beautiful green.
Reflections rarely match the body they meet
A yellow sphere d f g e struck by the blue object b c is tinged green rather than showing either pure hue, because b c is lit by the air or by colour. Two small pen diagrams of spheres receiving coloured rays illustrate the argument.