What technique did Leonardo da Vinci use to achieve unprecedented realism and depth in his paintings?

Sfumato

Leonardo da Vinci revolutionized the art of painting with his technique of sfumato, which allows for smooth transitions between colors, thus mimicking the way the eye perceives contours and shadows in nature. This method creates a sort of "smoke" or blur that gives his works a dreamlike and mysterious quality. Sfumato is particularly evident in the Mona Lisa, where the enigmatic smile and penetrating gaze seem to emerge from the shadows and light. This technique marked a turning point in art history, influencing many artists after Vinci.