Mona Lisa

By 1666 this panel was hanging in the Alcázar, the royal palace in Madrid, and the inventory clerk entered it as a portrait by Leonardo da Vinci's own hand. Sometime after 1750 somebody painted the entire background out in flat black, and for the next two centuries it looked like one more dark, tired copy of a famous face.

The black came off in 2011 and 2012, and the landscape underneath had survived intact, blue rock towers, winding water, a balustrade with a small column at either side. The museum's author line is Workshop of Leonardo da Vinci, meaning a hand working beside the master rather than after him. The names put forward run from his Milanese pupils to two Spanish painters who were in Florence in those same years, Fernando Yáñez de la Almedina and Hernando de los Llanos. The Prado names none of them, and dates the panel between 1507 and 1516.

The support is walnut, an expensive wood of the kind Leonardo used himself. What this version keeps, and the one in Paris no longer shows through its old varnish, is the colour of her red sleeves and the fine hairs of her eyebrows.