Nondestructive evaluation of delaminations in fresco plaster using transient infrared thermography

A transient method of thermal nondestructive testing is applied to detect subsurface delaminations in fresco plaster as a part of restoration work that is being conducted in Italy. A two-dimensional cylindrical model is used to estimate temperature distribution in materials with defects of various sizes and depths. The possibility of testing plaster with thickness up to 30 mm is illustrated. The choice of heating technique, which is supposed to be really nondestructive to ancient frescoes and powerful enough to create reasonable temperatures signals, is considered. Test duration and optimum sampling interval are discussed also. The structural noise of plaster and the influence of surface painting are investigated.