Castiglione seems to have invented the technique of monotype, a hybrid of drawing and printmaking. He explored both basic methods, the 'positive' in which the artist works up the image directly on a metal plate with sticky printer’s ink, and the 'negative' in which the plate is coated in ink and the light tones of the image are scraped away. Only 25 or so of Castiglione’s monotypes are known, unique in the seventeenth century; the technique then lay dormant until William Blake independently hit upon the same process, but it was not until the late nineteenth century that artists such as Degas and Gauguin fully exploited its potential.