Monitoring of historical stucco using a structured-light 3D scanner at the Château de Germolles
The aim of the collaborative project between the i3mainz and Sarl Germolles, represented by Professor Christian Degrigny, is to detect, analyze and document the changes and deformations of the stucco applications of the dressing room of Margaret of Bavaria over the course of several survey periods.
In the heart of Burgundy, not far from Beaune and Chalon-sur-Saône, lies Château de Germolles, the best-preserved residence of the Dukes of Burgundy. Built in the second half of the 14th century, this estate reflects an important page in the area’s history. The castle is also one of the few surviving examples of residential design in France in the 14th and first half of the 15th centuries, as most of the princely palaces from that period have disappeared. (Wikipedia)
The dressing room of Margaret of Bavaria is one very well-preserved part of the palace. Particularly noteworthy here are the very beautifully decorated walls with murals and stucco elements dating from the time.
In historical buildings like the above-mentioned chateau, materials of different types and quality were often used. Due to the unique state of preservation, it is difficult to analyze these materials without damaging the respective elements. However, since movements and deformations can occur as a result of the architectural construction, the material used or external influences (temperature, humidity), it is of great interest to pinpoint and analyze these deformations. This enables inferences to be made about the causes of cracking or similar phenomena. In the Château de Germolles, precisely such phenomena (cracking, flaking) are occurring in the dressing room of Margaret of Bavaria mentioned above. They are mainly located in the stucco section of the ceiling. The aim of the collaborative project between the i3mainz and Sarl Germolles, represented by Professor Christian Degrigny, is to detect, analyze and document the changes and deformations of the stucco applications over several survey periods. Due to the expected deformations, which will primarily be in the sub-millimeter range, a measuring system must be selected that is capable of scanning the application surface in sufficient detail, as well as providing the accuracy to detect geometric changes of a few tenths of a millimeter. Based on the requirements, the three-dimensional recording of the stucco surface is performed using active stereophotogrammetry. A close-range scanner manufactured by GOM with a spatial resolution of 0.2 mm and a depth accuracy of approx. 0.05 mm (depending on material and surface conditions) is used here. To be able to make a statement about possible changes in the stucco due to temperature influences, for example, a total of four survey periods will be carried out at different times of the year.
In a first survey period in June 2018, the baseline measurement for the following measurement surveys was performed. To guarantee stable and comparable measurements over the total of four surveys, permanently attached reference points are necessary. They were installed in the entire stucco area in cooperation with Christian Degrigny, the on-site restorer, prior to the actual measurement process. As these points are not only used to support the measurements performed by the structured-light 3D scanner, but also to link the individual measurement surveys, it is necessary to determine the coordinates of the reference points photogrammetrically prior to the scanning process. The entire stucco area can be recorded by combining multi-image photogrammetry and active stereophotogrammetry.
The second survey period was timed to coincide with the start of the heating season at the Château de Germolles. Here, it was examined whether these temperature-related climate changes were affecting the stucco.
The first measurement survey provides the geometrically highly accurate baseline for monitoring, in the form of a digital 3D model of the stucco applications in their entirety. After the measurement of the stucco in the second survey, a first comparison with the data of the previous survey is possible.