Sfumato (Italian: 'smoked' or 'faded') is Leonardo da Vinci's signature technique of blending tones and colours so subtly that outlines dissolve into shadow. Where earlier Renaissance painters defined forms with crisp outlines, Leonardo built up thin, translucent layers of glaze — sometimes fifty or more — to create transitions imperceptible to the human eye. The result is that faces seem to exist in a perpetual half-light: expressions hover between two states, never fully legible. The Mona Lisa's famous smile is the supreme example — it shifts depending on where your eye is resting. Sfumato was never truly taught or transmitted; it died with Leonardo. Later painters attempted it, but none matched his ability to make light itself seem uncertain.