dyestuff, coloured brown with a trace of violet, that is obtained from a pigment protectively secreted by cuttlefish or squid. Sepia is obtained from the ink sacs of these invertebrates. The sacs are speedily extracted from the bodies and are dried to prevent putrefaction. The sacs are then dissolved in dilute alkali, and the resulting solution is filtered. The pigment thus obtained is precipitated with dilute hydrochloric acid and is then washed, filtered, and dried. The chemically inert pigment is fairly permanent and is used as a drawing ink and as an artist's watercolour, particularly in monochrome.

As a type of ink, sepia has been known at least since ancient Roman times. Only from Renaissance times onward, however, did sepia become popular as a drawing medium. In the late 18th and 19th centuries it was particularly popular and generally replaced bistre as a medium for making wash drawings. As a primary pigment, it has been superseded in the 20th century by industrially manufactured watercolours.