The main material is the stone (lithos in Ancient Greek). The artist draws with special crayons, pencils and liquids (similar to watercolour) that contain grease, before using an etch mixture to fix the drawing onto the stone with a chemical reaction. The process is repeated for each layer of colour.

It sounds complicated, but relies on a simple technique. “The three main materials are stone, grease and water, as the entire printing process depends upon the principle that grease and water don’t mix,” says Dudley. “Essentially you can draw with anything that contains grease – one artist we know drew a lithograph using butter. Fingerprints and petroleum jelly body prints work nicely as well.”

The big reveal

An artist who took an unconventional approach to lithography was Francisco de Goya. One of his companions, the Spanish painter Antonio de Brugada, wrote about Goya’s unorthodox working method: “The artist worked at his lithographs on his easel, the stone placed like a canvas. He handled the crayons like paintbrushes and never sharpened them. He remained standing, walking backward and forward from moment to moment to judge the effect.

“He usually covered the whole stone with a uniform grey tint, and then removed the areas that were to be light with a scraper; here a head, a figure, there a horse, a bull. The crayon was then brought back into play to reinforce the shadows and accents, or to indicate figures and give them a sense of movement.”

It’s a layered process, which is often partly hidden from the artist until the final reveal. Dudley says her favourite part is “the moment when we take the first print off the stone that carries the drawing for the final colour in a multiple-layer image… you still don’t really know how it will look until you see it printed. Then you ink up the last stone, lay the first sheet down and run it through the press. The anticipation of seeing the first complete print is often palpable. It’s almost like a ‘Eureka’ moment once you see the first complete image.”

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