Lecture Diagram 58: Perspective Construction of Pulteney Bridge, Bath (after Thomas Malton Junior)

This image on white wove paper with a Whatman watermark and countermark of 1808 was largely created with graphite pencil ruling, with some freehand drawing for small curved elements. A grey/black ruled wash has been used for the buildings. Other lines were drawn lightly in pencil and then had a red wash added.

Many of the ruled lines have been incised lightly with a sharp point, probably an engraving tool. This means that this image was used as the original for a copying process which Turner used to generate a limited number of copies from other lecture diagrams. He needed several copies so that he could if he chose illustrate the drawing of a single element such as a column alone, then later with perspectival lines going to a single point, or built up to a colonnade of identical columns, or used to illustrate the way to make a column look three-dimensional by shading, He could also use such a colonnade to form an entire elevation of the building. The process seems to have involved placing a blank sheet on a table, overlaying double-sided copying paper, followed by another blank sheet, another sheet of double-sided copying paper, and the image to be copied. Then he pressed down hard on each ruled line of the top copy with a sharp tool run against a ruler, and unpacked the paper stack to reveal one good and one pale copy, with little smudging on the ‘good’ side. If necessary, he strengthened straight lines in the copies, which would both be identical and not reversed, and then he hand-applied the curved elements freehand as necessary and/or painted the lines to make them bold enough to demonstrate to a large audience in a room lit artificially.

Recipes exist for home-made copying paper, and evidence from three groups of the lecture diagrams – smudges of black material, occasional smears and the incised lines – suggests that a mixture of egg yolk or whole egg with cheap lamp black was involved. Thin paper dipped in such a watery solution, left to dry, and used once, would have worked. The copying papers were not used repeatedly, since all the copied lines are crisp and even, therefore clearly made from virgin copying paper that was so cheap it could be discarded after one use. This process could have been done at home, and repeated on a top copy if more copies were required. There is precedent for using eggs too: a fair proportion of the primed canvases Turner used while his father was alive and assisting him in the studio carry a priming made from lead white and whole eggs. Possibly Turner’s father assisted with the copying as well.