The process of Lithography was discovered by Alois Senefelder in Bohemia two hundred years ago in 1798. However, it was not until the late 19th century that its true potential was exploited by the post impressionists and great poster artists like Toulouse-Lautrec.
Lithographic prints are taken from a flat surface, traditionally Bavarian Limestone, although nowadays zinc plates are often used. The image is drawn onto the prepared surface of plate or stone with a greasy crayon or greasy ink. The surface is then moistened with water, whereupon the parts not covered by the crayon or ink become wet, while the areas where the greasy drawing is made repel the water and remain dry. The printing ink which is then applied with a roller adheres only to the drawing,being repelled by the wet parts of the stone. The stone or plate is then placed on a lithographic press and ink is transferred from it to the paper by direct pressure, or in the case of offset printing, first to a rubber blanket then onto the paper.
Normally one plate is used for each colour. Exceptional care is taken to place the paper in exactly the same position on each subsequent stone or plate (registration). Using the tradional method this is achieved by making a tracing of the original drawing which is then transferred to each subsequent stone.
Since 1988 I have used a more recently developed 'light box method' for making lithographs. Here the need for tracing between colours is rendered unnecessary. Working on top of a light box the image is applied (drawn, painted, wiped etc.) onto a sheet of clear grained plastic using any medium that will take to it, even charcoal. This allows the artist greater flexibility plus the option to alter (rub out) marks during that process - very difficult with traditional methods as once grease is applied to a stone or plate it can be removed only by considerable processing, which puts the image at risk. An aluminium plate with a light sensitive coating is placed over the plastic in a light exposure unit. Exactly the right amount of light is shone through the plastic onto the plate, thereby altering its chemical composition in those clear undrawn areas. The drawn areas resist light leaving an unsensitised, undeveloped coating on the plate as an exact 'reproduction' of the 'drawing'. This method is extremely receptive to all the nuances of the original image.