The Lithographic printing technique was originally developed with the use of flat porous stone plates, commonly limestone. In fact, the word ‘lithograph’ historically means ‘image from stone’.
The modern Offset Lithographic printing technique is practised using metal plates. Based upon the principle of oil and water working in repulsion, the area of the printing plate that is not to be printed is kept moist by water and humidity at all times. When the plate is introduced to the oil based printing ink, the areas filled with water naturally reject it and ensures that non-printing areas remain ink free. The inked image is then transferred (or ‘offset’) from the plate to a rubber blanket, which is the transferred to the printing surface.