On May 14th, two of our professionals, Dr. Leszek Krzemień and Dr. Marcin Strojecki, contributed their knowledge and skills to evaluate the condition and necessary conservation treatments for Hans Dürer’s painting from 1526, “Saint Jerome Penitent”. The painting, made using a tempera technique on wood, belongs to the collections of the National Museum in Krakow. The study was performed using a non-contact, non-destructive method called laser interferometry (DESPI – Digital Electronic Speckle Pattern Interferometry), which is a variation of holographic interferometry based on the analysis of laser light scattered from an optically rough surface.
How does it work?
Two beams take part in the interference process: the first illuminates the examined surface, and the reflected light interferes with the second reference beam. Analysis of the resulting fringes allows for the identification of surface defects (irregularities) such as blisters under the decorative layer or microcracks. The surface can be excited for observation in two ways. If the surfaced is heated about 2-3 ºC using a 300 W photographic lamp, the spatial distribution of deformations caused by heterogeneity in the temperature distribution can be recorded. Alternatively, sound can be used to vibrate the surface and reveal detached parts of the object which move in contrast to well adhered stationary zones.
The measurements detected and localized damages such as cracks and detachments of paint layers from wooden boards. The description of the condition of the polychromy of the image will be used in the future to assess the effectiveness of applied conservation techniques.