Chromolithography is a unique method for making multi-colour prints. This type of colour printing stemmed from the process of lithography, when chromolithography is used to reproduce photographs, the term photochrome is frequently used. Lithographers sought to find a way to print on flat surfaces with the use of chemicals instead of relief or intaglio printing, hand-colouring also remained important, elements of the official British Ordnance Survey maps were coloured by hand by boys until 1875. The initial technique involved the use of multiple lithographic stones, one for each colour, depending on the number of colours present, a chromolithograph could take months to produce, by very skilled workers. However much cheaper prints could be produced by simplifying both the number of used, and the refinement of the detail in the image. Cheaper images, like advertisements, relied heavily on a black print. The process is based on the rejection of grease by water, 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 unfortunately corrodes easily, 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 desensitize the surface. Before printing, the image is proved before finally inking up the image with oil based transfer or printing ink, the inked image under pressure is transposed onto a sheet of paper using a flat-bed press. This describes the form of printing. The offset indirect method uses a cylinder that transfers the image from printing surface to the paper. Colours may be overprinted by using 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, ben-Day medium, uses a raised gelatin stipple image to give tone gradation. An air-brush sprays ink to give soft edges and 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 position, each stone or plate must be precisely ‘registered, ’ or lined up. Chromolithographs are considered to be reproductions that are smaller than double demi, autolithographs are prints where the artist draws and perhaps prints his or her own limited number of reproductions. This is the true art form
Uncle Sam Supplying the World with Berry Brothers Hard Oil Finish, c. 1880. This cheaply produced chromolithographic advertisement employs a technique called stippling, with heavy reliance on the initial black line print.
1872 chromolithograph of roadside inn, published in Maryland