Semicircular transfer grids

Using the infrared camera, conservators detected traces of graphite under the paint layers on several mural panels. These traces are part of a transfer grid, such as this grid on Judgment. The rays and arches naturally divide the semicircular surface of the lunette into regular segments. The rays originate in a central point at the bottom edge of the composition and intersect successive arches extending to the curved upper edge of the canvas.
 
The Triumph of Religion