A painter should begin every canvas with a wash of black, because all things in nature are dark except where exposed by the light.

The saying expresses a core Renaissance insight into chiaroscuro: form becomes visible not because objects are inherently “bright,” but because light reveals them against an underlying field of shadow. Read as practical advice, it urges painters to think tonally—establishing the darkest values first so that highlights can be built as the consequence of illumination. More broadly, it frames vision as relational: what we perceive depends on contrast and exposure, not on absolute color. Whether or not Leonardo wrote these exact words, the idea aligns with his sustained interest in optics, shadow, and the modeling of bodies through gradations of light.