BARCELONA.- Shown in the Engraving Exhibition Rooms of the museum is a selection of lithographs by Pablo Picasso developed between 1945 and 1972, when the artist really developed his interest in this printmaking technique. As he usually did when exploring a technique, he used several kinds of plates - stone, zinc, transfer paper - and tried a variety of traditional media - grease pencil, pen, wash -as well as introducing new materials and radically transforming the old established practices of the craft.