Editing Chromolithography (section)

==Process==
Lithography, including chromolithography, is a process based on the rejection of water by grease. The image is applied to stone, grained zinc or aluminium surfaces, with a grease-based crayon or ink. [[Limestone]] and zinc are two commonly used materials in the production of chromolithographs, as aluminium production was limited before the invention of the [[Hall-Heroult process]]. After the image is drawn onto one of these surfaces, the image is gummed-up with a [[gum arabic]] solution and weak nitric acid to protect the remaining surface before inking up the image with oil based transfer or printing ink. Before final printing, the image is proof printed and any errors corrected. In the direct form of printing, the inked image is transferred under pressure onto a sheet of paper using a flat-bed press. The [[Offset printing|offset]] indirect method uses a rubber-covered cylinder that transfers the image from the printing surface to the paper. Colours may be overprinted by using additional stones or plates to achieve a closer reproduction of the original. Accurate registration for multi-coloured work is achieved by the use of a key outline image and registration bars which are applied to each stone or plate before drawing the solid or tone image. [[Ben Day process|Ben-Day]] medium uses a raised gelatin stipple image to give tone gradation. An air-brush sprays ink to give soft edges. These are just two methods used to achieve gradations of tone. The use of twelve overprinted colours would not be considered unusual. Each sheet of paper will therefore pass through the printing press as many times as there are colours in the final print. In order that each colour is placed in the right position, each stone or plate must be precisely 'registered,' or lined up, on the paper using a system of register marks.<ref name="temple2007"/>

Prints described as chromolithographs are typically smaller than posters and advertisements, both common types of colour lithographs in the later 19th century and subsequently, and are of finer quality, generally suitable for framing as prints. Autolithographs are prints where the artist draws and perhaps prints his own limited number of reproductions. This is the true lithographic art form.<ref>"[http://rmc.library.cornell.edu/ornithology/exhibit/exhibit5.htm Chromolithography."] ''Beautiful Birds Exhibit''.1999. Cornell University Library. 11 April 2007.</ref>