Digital speckle pattern interferometry for the condition surveys of painted wood: Monitoring the altarpiece in the church in Hedalen, Norway

Digital Speckle Pattern Interferometry (DSPI) and Speckle Decorrelation (DIC) were used in condition surveys of a wooden altarpiece in the church of Hedalen, Norway. Two surveys were conducted, one before and one after the heating season in the church to trace the possible development of damage in the paint layer caused by relative humidity variations induced by the heating system. The measurements demonstrated that the speckle techniques can contribute to detecting irregular areas on the paint surface and in the paint structure. They proved particularly effective in tracing paint detachments at an incipient stage which cannot be easily detected by an unaided eye or manual inspection. The results of the speckle techniques may thus guide a traditional conservation survey, or the use of further microscopic or analytical survey techniques. The speckle techniques could be routinely used by conservators who are not scientists if simple, portable instruments were available on the market.