The Feasibility of using Thermography to Detect Subsurface Voids in Painted Wooden Panels

Abstract

Thermography is a technique whereby the construction or condition of objects is studied by means of precisely measuring temperature variations over the surfaces of such objects. Voids within solid structures tend to cause cold or hot spots on the surfaces of these structures as the whole object is heated or cooled slightly. Industrially, thermography is used to detect voids in cast and laminated structures. By studying areas of known voids in test panels, the described research indicated that voids as small as 1/8″ in diameter beneath the gessoed surfaces of wooden panels could be resolved with a raster scanning radiometer, the principal instrument used for thermographic studies. Smaller voids were discernible when they were grouped together. Only voids immediately beneath the gessoed surfaces of the test panels were detectible. Additional tests indicated that areas of simulated cleavage between the wood support and the gesso layers on the test panels could be detected thermographically.