Lithography

Invented in Bavaria in 1798, lithography is the only process which does not rely on a physical difference between the image and the non-image areas. It is a chemical process which relies on the antipathy between grease and water.

A block of limestone is prepared by grinding carborundum powder and water into its surface using a heavy metal disc- the levigator. The resulting flat, grained surface can then be drawn on using materials with a high grease content. Alternatively, rather than draw directly onto the stone, the artist can draw onto specially prepared transfer paper.

When the drawing is complete the entire surface of the stone is treated with a solution of gum arabic and nitric acid. This causes the image and non-image areas to become chemically separated, and when a roller charged with greasy ink is passed over the dampened stone, the ink will attach itself to the image and be rejected by the background. Paper is placed face down on the inked stone and is passed through the press under considerable pressure, transferring the image to the paper.