Lithography begins with a particular type of limestone block polished down to a fine flat even grain. An image can then either be drawn directly onto the stone, or transferred to it, by using a variety of materials ranging from crayons to washes as long as they contain grease or oils (lipids). When the drawing is etched with acid emulsified in gum Arabic a chemical reaction takes place in which a salt layer seeps into the stone’s pores around the image. When the image is washed off and the stone dampened, the water is only attracted to the salty layer created by the acid etch. When rolled with a stiff oil-based ink, the ink will coat the stone only where the water in the surface pores do not repel it recreating an image identical to the original drawing. This image is then capable of being transferred onto paper through the pressure of a press, and then the dampening and inking process can be repeated over and over to produce multiple images. The crayon drawn look so common in lithography was almost never used on postcards. Lithography however was commonly used on postcards in the form of chromolithography, black & white halftones, tinted halftones, tricolor printing, process printing, and offset printing.
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