Castiglione seems to have invented the technique of monotype, a hybrid of drawing and printmaking. There are two basic methods, a ‘positive’ in which the artist works up the image directly on a metal plate with sticky printer’s ink, and a ‘negative’ in which the plate is coated in ink and the light tones of the image are scraped away with a stick or cloth. A piece of dampened paper is then placed over the plate and run through a press to give a single strong print (though a couple of subsequent weaker pulls, such as cat. 77, can be obtained).

The technique produces dramatic effects of light and dark, and Castiglione employed both positive and negative methods, sometimes in combination, to create images that are unique in the seventeenth century. The art of monotype then lay almost dormant for 250 years, until artists such as Degas and Gauguin revived the technique.