Lithography – which means, literally, ‘stone drawing’ – is a printing method that uses a flat polished stone or metal plate and is based on the notion that grease and water don’t mix.
It was developed in the late 18th century, initially using Bavarian limestone for commercial printing of musical scores – although aluminium is often used today.
A drawing is made on the stone or plate using a greasy crayon or ink. A solution of gum arabic and nitric acid is then applied over the entire surface, ‘fixing’ the design on to the stone. Water is applied to the plate and is absorbed everywhere except where repelled by the greasy image.
A roller dipped in oil-based ink is then rolled over it, with ink only sticking to the greasy areas. The image is transferred on to paper lightly via a printing press, creating neither a raised nor embossed effect but one where the ink lies entirely on the surface of the paper. The design may be produced in one colour from a single stone, or divided among several stones to create, via multiple printing, a litho in more than one colour.