To make paint from azurite, the rocks are collected, sorted, and refined, keeping only the bluest parts. These are crushed and ground into a fine powder. The powdered azurite is mixed with a liquid binder, typically egg white for painting on parchment, or egg yolk for painting on wooden panels, to make a paintable mixture. The backgrounds in the manuscript leaf depicting St. Lawrence, and many other of the Laudario leaves as well, were painted with relatively coarsely ground azurite to give them a brilliant deep blue color. When you look at one of these passages under the microscope, it indeed looks like a field of blue rocks.