The holographic techniques provide a detailed topographic map of a work's surface and any underlying surface damages, which can be used: 

 

A) to diagnose the state of the work, and the relevant preventive or restorative methods that need to be applied to avoid further deterioration

 

B) to accurately compare the "first" topographic map to later topographical maps of the work, for example after an exhibition of the work or after the work has been loaned to another museum.

There are various holographic techniques, but the most widely used one is the holographic interferometry technique. With this technique the object is exposed to an infrared source which heats it for a few seconds. Afterwards a probe laser captures the object's vibrations as it returns to its original state.