Zprávy památkové péče 2018, 78(5):504-510 | DOI: 10.56112/zpp.2018.5.11

Survey of interior plasters of the Upper Castle in Bečov nad Teplou

Petr Kuneš, Dagmar Michoinová, Vladislava Hůlková

NPÚ, GnŘ

The article presents the results of the material-technological study of plasters from the donjon area and the connecting structure of the Upper Castle in Bečov nad Teplou. In the interiors of the Upper Castle, a wide range of plasters have survived to varying degrees; they span the castle's entire historical development, from the second half of the 14th century to the period of the youngest utilitarian modifications from the 18th century. In this study, samples of most of the identified types of plasters and mortars that cover these periods were examined. The mortar analysis showed that all mortars examined contain very similar aggregates that correspond to the local source of sand in their mineral presence. This sand is predominantly the product of degradation and transfer of mica granite and contains quartz and feldspar, predominantly plagioclases, muscovites, and biotite. The individual mortars differ by the width of the aggregate distribution, in particular by its roughness and the content of the aluminum phase. Particularly the fine-grained plasters which served as substrate for paintings were made of aggregate whose roughness was probably adjusted by sieving. From the binder point of view, all of the cases examined are lime mortars, with the exception being only clay mortars or plasters. These exceptions came from utilitarian interior modifications in the 18th century, when the castle served as a granary. An interesting finding in the Gothic mortar, which helped clarify the type of binder and determine the probable source material for lime leaching, was the discovery of marble grains. Grains of unfired calcite are present in the samples of Gothic plaster and exhibit a more or less extensive conversion to micrite and can therefore be uniquely associated with the process of lime production. Natural sources of limestone rocks almost do not occur in the vicinity of Bečova nad Teplou; the only significant deposit of crystalline carbonate is a small karst area near Lázně Kynžvart, approximately 20 km southwest of Bečov nad Teplou. Historical pit mining marble is documented in this area, so it seems likely that rock from this site was used for lime burning for the oldest mortar of the castle. The preserved plaster of Bečov Castle provides proof of the materials used, the working procedures, and the aesthetic and utilitarian demands of the building's owners. Plasters are also a source of information on building developments and long-extinct buildings; they also bear valuable paintings, a number of inscriptions, and other traces of the past. Despite the minimal care devoted to them and the castle in the past centuries, they still show extraordinary durability and functionality and still fulfill their role in the building system after six hundred years. They protect the masonry from moisture, salination, and mechanical damage, and they contribute to the stabilization of the indoor climate of the building. Their aesthetic effect, which contributes to the unique atmosphere of the castle, also plays an unmistakable role. The results obtained by the material technology survey are useful for proposing compatible materials for preserving and supplementing plasters, and in some cases it has been possible to use them to specify the sources of the materials used and to more precisely distinguish the individual building phases.

Keywords: Bečov nad Teplou, Upper Castle, interior, plaster, exploration, material analysis, lime, stone

Published: December 1, 2018  Show citation