Stiacciato

Stiacciato is a technique which allows a sculptor to create a recessed or relief sculpture with carving only millimetres deep.[1] To give the illusion of greater depth, the thickness gradually decreases from the foreground to the background. In some ways it is more similar to a 2D image than a 3D sculpture and so the relief can use perspective. Vasari writes of the technique:

The third types are called bas- and stiacciati-relief, which have nothing in them but drawing the figure with dents and schiacciato relief. They are very difficult if there is a large amount of drawing and invention involved, because it is hard to give these things grace thanks to the mode's love of contours. And Donato [ie Donatello] worked best of all sculptors in this genre, with art, drawing and invention. We see many of this kind [of sculpture in the form of] highly-figured ancient Aretine vases, masks and other ancient works; and similarly in ancient cameos and in bronze-stamping cones for medals and coins.

Donatello's schiacciato work Herod's Banquet, Siena Baptistery.

The technique was mainly used in the 15th and 16th centuries, begun and dominated by Donatello.[2] The earliest surviving example is his St George Freeing the Princess (1416-1417) and his other works in the genre include the Pazzi Madonna (1430), The Assumption of the Virgin (Sant'Angelo a Nilo, Naples, 1426-1428) and Herod's Banquet (Siena Baptistery, 1423-1427).

References

1. http://www.treccani.it/enciclopedia/stiacciato/
2. Rolf C. Wirtz, Donatello, Könemann, Colonia 1998.