As a young artist, Leonardo learned how to draw using metalpoint – a stylus of lead, silver, copper or other metals. Lead can mark untreated paper, but harder metals require the paper to be coated with a slightly abrasive preparation of ground bone ash, mixed with dilute glue to bind it to the paper. Artists often added a pigment such as indigo or red lead to colour the paper. Leonardo abandoned this laborious technique in the 1490s, and it soon fell out of use across Italy.