Wandmalerei

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Autoren: NN

Einleitung

Wall paintings, from prehistory to the present day, comprise a major part of our cultural heritage. One of the most common deterioration problems affecting wall paintings is salt damage, caused by interactions between soluble salts, the environment and the material properties of the object. The susceptibility of wall paintings to salt weathering is due to the fact that, to a greater or lesser extent, they are porous. This characteristic allows moisture exchange with their surroundings, and consequently they are prone to contamination by soluble salts. Moreover, wall paintings are particularly vulnerable to salt damage because the paintlayers are located at the interface between the external environment and the microclimate within the wall. Consequently, the painting and its immediate support form the primary site for evaporation and salt accumulation. Owing to the ubiquitous presence of salts worldwide, this type of damage is one of the most widespread and commonly encountered in wall paintings conservation. Unfortunately, it is also one of the most pernicious and intractable. The term ‘wall painting’ covers a great diversity of objects, and is not limited to those on vertical surfaces, but includes paintings executed on walls, ceilings, and other architectural forms. The key feature of a wall painting is that the structure in which it is housed forms an integral component of the painting itself. This support structure can take many different forms, from built structures to excavated rock cut or subterranean structures, and entirely natural formations—as in the case of cave paintings. In addition to porosity, these objects are united by the fact that they are irremovable and require conservation in situ. This has important implications for the amelioration of salt deterioration problems. A methodological approach is required which fully takes into account not only their complex structure and material composition, but also the environmental conditions to which they are exposed. In the case of artworks located within historic buildings this demands that a balance is sought between the needs of the object, and the building users.

Schadensbilder an Wandmalereien

In general, the type of damage caused by solule salts to wall paintings is related to the location of their crystallisation. The nature of the damage varies widely—but can be broadly divided into two main categories: efflorescence (salt crystallisation at the surface) and subfluorescence (salt crystallisation beneath the surface of the object). Although visually alarming, efflorescences are generally regarded as less harmful than subflorescences, which cause the disruption and loss of the object's surface. In the case of a wall painting, the surface of the wall is the object, and the consequences of subflorescence are extreme. In addition, soluble salts also contribute indirectly to decay processes by increasing the object's moisture content, promoting the alteration of water-sensitive materials.