Litography

Lithography (from Ancient Greek , lithos, meaning 'stone', and , graphein, meaning 'to write') is a method of printing originally based on the immiscibility of oil and water. The printing is from a stone (lithographic limestone) or a metal plate with a ball grained surface. It was invented in 1796 by German author and actor Alois Senefelder as a cheap method of publishing theatrical works. Lithography can be used to print text or artwork onto paper or other suitable material.

Lithography originally used an image drawn with oil, fat, or wax onto the surface of a smooth, level lithographic limestone plate. The stone was treated with a mixture of acid and gum arabic, "etching" the grease content of the drawing material into the pores of the stone and chemically creating grease reservoirs. The open stone (without drawing) was affected by the gum arabic creating a thin gum layer that would then attract water. When the stone was subsequently moistened, these gummed areas retained water; an oil-based ink could then be applied with a roller sticking only to the original drawing. The ink would finally be transferred to a cotton fine art paper sheet, producing a printed page. This traditional technique is still used as a fine art medium today.

In modern lithography, the image is made of a polymer coating applied to a flexible plastic or metal plate. The image can be printed directly from the plate (the orientation of the image is reversed), or it can be offset, by transferring the image onto a flexible sheet (rubber) for printing and publication.

As a printing technology, lithography is different from intaglio printing (gravure), wherein a plate is either engraved, etched, or stippled to score cavities to contain the printing ink; and woodblock printing or letterpress printing, wherein ink is applied to the raised surfaces of letters or images. Today, most types of high-volume books and magazines, especially when illustrated in colour, are printed with offset lithography, which has become the most common form of printing technology since the 1960s.

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