Guild procesion of lithographers in Strasbourg, France, 28th June, 1840.
© Science Museum / Science & Society Picture Library
'Cortege Industriel de Strasbourg', ('Strasbourg Industrial Procesion'). Guild procesion of lithographers with French flags. Lithography, discovered in 1796 by Alois Senefelder (1771-1834), whose bust is carried by the workers. The technique relies on the repulsion of oil and water to print from a flat surface, originally Bavarian limestone. A greasy crayon is used to sketch on the stone, which is then sponged with gum solution. The gum is repelled by the grease, making the undrawn areas ink-repellent. The stone is placed on the pres, inked, paper laid on it, and the wheel turned to draw it under a bar which preses down to make the print.