On the south side of the Piazza del Duomo in Pisa, housed in a former hospice, is the Museo delle Sinópie (opened 1979). During the restoration of the Camposanto a large number of these preliminary sketches for frescoes (sinópie) were discovered, and these are now displayed in the museum.

These sketches were the artist's most important contribution to a fresco, specifying as they did every detail of a composition; thereafter the actual execution of the fresco was often left to pupils or assistants. In the museum the sinópie are shown in conjunction with reproductions of the corresponding frescoes. Sinopias are the preparatory drawings for frescoes done directly on the wall. One of the explanations for the development of this technique is the lack of large quantities of paper or other similar materials during the XIV century.

The drawings were done in small size, directly onto the next to the last coat of plaster. The artists used a brush dipped into a red-earth pigment from Sinope, a city in Asia, hence the name "sinopia". These drawings were then covered with a layer of rough and fine sand onto which the sinopias were permanently hidden.