For the article on printing, Diderot turned to Mr. Brullé, the foreman of the shop where the Encyclopédie was printed, for a practiced tradesman’s account of the process by which letterpress type is set and readied for the press. The first of the accompanying plates shows the composing room where lines of raised, movable metal type are set, proofed, and arranged into pages. In a masterful didactic touch, the page facing the illustration of set type shows the positive text that results when the inked lines, which are always composed in reverse, are put through the printing press.
The Encyclopedists borrowed liberally from several sources for the texts and images they published, but much of their work was based on direct observation or expert testimonial. Louis-Jacques Goussier, Diderot’s chief assistant for the mechanical arts, completed his descriptions and illustrations of papermaking after spending weeks at the l’Anglée paper mill near Montargis. Papermaking requires unlimited supplies of water, and the plate shows the canal system established to divert water from a nearby river to the factory and to power the mills inside.
The ambition to record the mechanical arts accurately resulted in some remarkable images. The plate showing the slate mines in the Meuse River Valley depicts the steeply tilted shafts required to reach the region’s best quality slate. The result is a striking picture that evokes the uncomfortable conditions in which the miners worked.