Castilian or Aragonese School. 15th Century. 'The Mass of Saint Gregory' Oil on panel. 96 x 69 cm. The composition depicts Saint Gregory kneeling before the altar at the moment of the Consecration, with the vision of Christ as the Man of Sorrows, surrounded by the instruments of the Passion. This was the sign used to convince and convert a heretic of their disbelief in transubstantiation. To the left of the scene are two figures that are likely to be the donors.