French scientists studied Leonardo da Vinci's painting techniques by analyzing seven of his paintings, including the Mona Lisa, without needing samples. They found that da Vinci painted up to 30 ultra-thin layers of paint and glaze to achieve subtle effects. This "sfumato" technique gave his works a hazy quality and created an illusion of depth. The analysis showed da Vinci was constantly experimenting with pigments, using manganese oxide for some shades and copper for others. The results provided new insights into da Vinci's innovative painting methods.