Leonardo da Vinci was a pioneer of 'sfumato,' an artistic technique that involves the subtle blending of colors and tones to create a soft, hazy transition between shapes. The word comes from the Italian 'sfumare,' meaning 'to evaporate like smoke.' Leonardo described it as painting 'without lines or borders, in the manner of smoke.' This technique is what gives the 'Mona Lisa' her famously enigmatic expression; by blurring the corners of her eyes and mouth, Leonardo left her emotions open to interpretation. Sfumato was a departure from the sharp, hard outlines of earlier Renaissance art and allowed for a greater sense of three-dimensional volume and atmospheric depth. It required the application of many thin layers of translucent glaze, a painstaking process that resulted in some of the most lifelike portraits in history.