These four plaques are made from pietre dura and pietre tenere, the grounds in pietra paesina. The conservation required only light cleaning and careful retouching of old repairs to some of the edges to improve their appearance.
'Pietra dura' (Italian for 'hard stone') is marble inlaid with designs in precious or semi-precious stonework. 'Pietre tenere' means 'soft stone'. 'Pietra paesina' translates as 'landscape rock', so named because of its decorative resemblance to landscape when it is sawn and worked.