An integrated study for mapping the moisture distribution in an ancient damaged wall painting

Abstract

An integrated study of microclimate monitoring, IR thermography (IRT), gravimetric tests and portable unilateral nuclear magnetic resonance (NMR) was applied in the framework of planning emergency intervention on a very deteriorated wall painting in San Rocco church, Cornaredo (Milan, Italy). The IRT investigation supported by gravimetric tests showed that the worst damage, due to water infiltration, was localized on the wall painting of the northern wall. Unilateral NMR, a new non-destructive technique which measures the hydrogen signal of the moisture and that was applied directly to the wall, allowed a detailed map of the distribution of the moisture in the plaster underlying the wall panting to be obtained. With a proper calibration of the integral of the recorded signal with suitable specimens, each area of the map corresponded to an accurate amount of moisture. IRT, gravimetric tests and unilateral NMR applied to investigate the northern wall painting showed the presence of two wet areas separated by a dry area. The moisture found in the lower area was ascribed to the occurrence of rising damp at the bottom of the wall due to the slope of the garden soil towards the northern exterior. The moisture found in the upper area was ascribed to condensation phenomena associated with the presence of a considerable amount of soluble, hygroscopic salts. In the framework of this integrated study, IRT investigation and gravimetric methods validated portable unilateral NMR as a new analytical tool for measuring in situ and without any sampling of the distribution and amount of moisture in wall paintings.

Comparison of GPR and unilateral NMR for water content measurements in a laboratory scale experiment

“…), which provides in situ water content measurements in a completely non‐invasive way (Capitani et al . ; Di Tullio et al . ) and it is particularly suitable to investigate flat solid surfaces or granular materials (Blümich et al .…”

“…Unilateral NMR is a portable technique, recently developed on the basis of the measurement principle used in well-logging (Blümich et al 2011), which provides in situ water content measurements in a completely non-invasive way (Capitani et al 2009;Di Tullio et al 2010) and it is particularly suitable to investigate flat solid surfaces or granular materials . Unilateral NMR is made of a u-shaped open permanent magnet Age 28 days ment conditions.…”

“…We then converted the NMR signal intensity into NMRestimated water content by using a calibration procedure described in a previous paper (Capitani et al 2009). Briefly, specimens were dried until reaching a constant weight and the intensity of the signal was measured.…”

Nuclear Magnetic Resonance, a Powerful Tool in Cultural Heritage

“…Portable NMR sensors have permitted the mapping of water distribution in historical walls and wall paintings [23,24]. Figure 3 shows a portable NMR sensor detecting moisture in an ancient wall painting affected by capillary rise of water from the ground.…”

Applications of Nuclear Magnetic Resonance Sensors to Cultural Heritage

“…Collected data were processed to obtain a contour plot where x and y were the coordinates of the measured area of the wall painting, and z was the integral of the NMR signal. The detailed procedure for calibrating moisture distribution maps has been reported elsewhere [38,39]. …”