The 'Grottensaal' of the new Palace in Potsdam, Germany ― Investigations for a conservation concept

摘要

The "Grottensaal" of the New Palace is a highly decorated hall with different pieces from nature like minerals, rocks, fossils and shells - thus, the hall looks like a grotto. Today extreme damage to the various decorative pieces is apparent and stems from salt crystallization. The aim of this investigation is to determine the weathering processes with non-destructive methods. Salt efflorescences were taken from the surface of the building materials and determined, the climate of the "Grottensaal" was measured and the moisture content of the walls was investigated using infrared-cameras. After monitoring the climate and the behaviour of the salts, it is possible to predict under which conditions the salts crystallize. The decay of the decorative pieces have been caused mainly by crystallization of the salt mirabilite (Na_2SO_4*10H_2O) and its transformation to thenar-dite (Na_2SO_4) and vice versa, which depends on the temperature and relative humidity. The results of the investigation lead to a conservation concept.