Authentication by the study of the structure of the materials present in the object
Techniques allowing an "in depth" vision of the materials
Reflectography
a. Principle :
infra-red rays, radiations similar to the visible light, are distinguished by longer wavelengths, penetrate therefore deeper into the material thus allowing to reveal elements subjacent to the visible surface
b. Applications :
in paintings, discovering of a pencil-sketch covered by a pictorial layer
Other techniques of "in depth" vision : radiography - gammagraphy