Unquestionably though, his most challenging project involved the Black Paintings of Francisco de Goya, which were painted in oil on the walls of Goya's home, the "Quinta del Sordo". The images were transferred from the wall to canvases, using pictures taken by the French photographer Jean Laurent as a guide. Many of the paintings were smudgy, badly cracked, and smeared with plaster, so he took the initiative of restoring them to their original state, as much as possible. The home's owner at that time, Baron Émile d’Erlanger, had planned to sell them at the upcoming Exposition Universelle (1878). By the end of 1875, only four of the fourteen paintings had been transferred. This very slow progress apparently prompted d'Erlanger to change his mind and donate them to the Spanish government instead.