Fingerprints of Leonardo da Vinci are visible on a painting

The version of The Virgin of the Rocks kept at the National Gallery bears fingerprints of Leonardo da Vinci. These traces were left during the execution of the brush sketch and the first undercoat, which corresponds to the painter's way of working. The rest of the work was however delegated to assistants, such as Giovanni Ambrogio de Predis or Marco d'Oggiono.