3.2.1. Photometric Stereo Normal Maps

In normal maps for all three prints produced through photometric stereo data, a large-scale deformation of the sheet within the region of the plate mark can be observed (Figure 10). Because this deformation only occurs within the plate mark indicating the boundary of the copperplate we propose that these deformations resulted from the application of high pressure to a wet sheet during printing. Smaller-scale deformations in the surface were more difficult to register due to the thickness with which the paint is applied

to the surface, but in plate 54 the printed lines are raised from the surface of the sheet (Figure 10), thus supporting the proposition that these were printed via an intaglio process.

**Figure 10.** Magnitude of the normal direction along the horizontal axis for plate 54 (**left**) and detail (**right**).
