Risk of damage to cultural property due to insufficient relative humidity in interiors of nationally valuable cultural property.

Due to global warming, Germany has been experiencing increased periods of heat with temperatures above 39 °C and significantly longer dry periods in summer for several years. These weather extremes will also increase in the future and sometimes have a damaging effect on the monument and its surroundings. While excessive humidity has been the problem in historic buildings in the past, critical values below 40% RH are now being measured more and more frequently indoors. These low humidities lead to a high risk of damage for numerous art genres. Especially polychrome surfaces, such as canvas paintings, paper and leather wallpapers, painted wooden surfaces as well as wall paintings, can suffer irreversible damage, such as cracking, loosening and loss of substance of the paint coating, etc.

The aim of the project "Under 40" is on the one hand to record and evaluate the climatically induced changes or the resulting damage to monuments by means of a national survey of the largest possible number of monument owners and managers. On the other hand, three case studies in Saxony and Saxony-Anhalt will be used to take a closer look at the indoor climate in various cultural monuments and to investigate its impact on the historical furnishings:

• Moritzburg Castle: The Baroque wall tapestries represent the largest inventory of Baroque leather wallpaper. 11 of the original 60 rooms in the palace are still preserved with the original wall decorations. The paintings, which depict Diana, the goddess of hunting, in the center, have been extensively restored in recent years and have since shown damage in the form of shrinkage cracks, which can be attributed to the extreme periods of heat. (Source, 27.04.2020, 12:41)
• Augustusburg Castle: in the castle church, the Cranach altar and pulpit from 1572 form one of the central exhibits of the castle museum. Painted by Lucas Cranach the Younger, the sacred painting shows the only surviving portrait of Elector Augustus and his family in the contemporary Renaissance décor. After seven years of restoration, the altar was equipped, among other things, with a climate box to record the slightest change directly on the sacred painting. (Source, 27.04.2020, 15:30)
• Albrechtsburg: Due to reparation payments from France, it was possible to completely renew the interior of Albrechtsburg Castle in Meissen towards the end of the 19th century. Starting in 1873, eleven artists painted the rooms on the first and second floors of Albrechtsburg Castle with history paintings, historical ceiling paintings and portraits. Due to the low humidity in the building, which is used as a museum, damage patterns such as loosening and loss of substance in polychrome color settings can also be seen in these wall paintings (Source, 29.04.2020, 13:30).

Using the data from the case studies and the information provided by monument owners and managers, it will be possible for the first time to compare the phenomenon of insufficient humidity across Germany and, ideally, to subsequently formulate suitable strategies for preventive damage control.