The materials used in the Prado panel are of high quality and the work is carefully painted. It is executed on a walnut panel, which was a support habitually used in works by Leonardo and his Milanese circle. It is to be found in Lady with the Ermine, La Belle Ferronière, and Saint John the Baptist. The panel does not have the traditional gesso underlayer. Instead it has a double preparation (an internal orangeish layer and an external whiteish one) principally made up of lead white. The results published in the last issue of the National Gallery Technical Bulletin (no. 32) on tests carried out on other works by Leonardo, such as Lady with the Ermine, La Belle Ferronière and The Archinto Portrait of Marco d’Oggiono reveal that although unusual, this type of preparation was used in Leonardo’s bottega when the support was a walnut panel.