Infrared Reflectography and Hiding Thickness

Infrared Reflectography

When it comes to the study of under-sketching rather than underpainting, scientific emphasis switches to infrared reflectography. X-rays are scarcely able to make any distinction between a plain chalk ground Fig. C.6 and one only slightly altered by addition of a thin sketch line in charcoal and bone black. But infrared radiation of wavelengths around 2.0 microns, having penetrated the upper paint layers, in particular the pigment, will be reflected at the level of the sketch and by virtue of...