1489 HISTORICAL PLASTER ON VILLAGE CHURCHES IN BRANDENBURG ARNOLD, B. srandenburgisches Landesamt tor Denkmalpflege, BrOderstr. 13, D-10178 Berlin, F.R.G.

BURGER, H. Brandenburgisches Landesamt fOr Denkmalpflege, Broderstr. 13, D-10178 Berlin, F.R.G.

NEUMANN, H.-H. Amtliche MaterialprOfanstalt Bremen, Paul-Feller Str.1, D-28100 Bremen, F.R.G.

WENS, R. Gesellschaft tor MaterialprOfung und Baustofforschung mbH, Plauener Str.163-165, D-1 ~ Berlin, F.R.G.

SUMMARY There is a large variety of historical plaster and mortars from the Middle Ages on Brandenburg village churches. These objects have been listed by the project group supported by German Federal Environmental Foundation. There have been investigations into the chemical , mineralogical and physical properties of several types of plasters. It occurs that in many cases historical plaster turned into gypsum, even though the surface seems to be "healthy". The process of turning lime into gypsum is due to air pollution and influence of climate. Often we find a complicated system of tiny cracks under the surface of the layer. These cracks mostly spread parallel to the surface and are filled with gypsum in several concentration and in several types of crystallization.

RESUME Dans le pays de Brandenburg apparaisse, en majorite sur les eglises en pierre, une multitude de crepis moyen-ageve. Au sein d'un project modele promu par la fondation allemande porei l'environnement sont ces expertises recensees dans tout le pays. Sur des objects selectionnes, les crepis sont releves et ensuite etudies sur leurs qualites physiques, chimique et mineralogiques. On constata alors, que meme crepis qui semblent a premiere vue intacts se sont transformes en platre a la surface. Le moyen original de liaison, le calque , s'est plus ou moins transforme en platre selon les influences climatiques et les incidences de l'environnement. Un systeme de fentes ramifees se deploie

a travers le crepi avec ses

structures en partie tres complexes. Ces fissures sont remfices de platre avec differentes concentration et avec differentes formes de cristallisations.

1. INTRODUCTION The village churches take an important part of cultural heritage in Brandenburg. Especially the churches from the Middle Ages, build during the 12th and 14th century, show a high quality in construction materials. Field stone has been the main building material. There is a large variety of historical plasters and mortars (elevated joints with simple or double scratchings, painted joints, friezes, ornaments on windows and doors) received. These findings are endangered not only by unprofessial conservation, but also by the environmental conditions (air pollution) . The historical mortars, plasters and renderings research are the theme of the interdisciplinary project between restorers, art historiens and scientists, supported by the German Federal Environmental Foundation. We began with a registration of churches with historic renderings in the whole country Brandenburg. Now there is achieved an overview of the existence and the damages of historic renderings.

1490 Then we have selected the churches with the most interesting findings from the point of view of conservators and scientists. There has been investigations into the mineralogical, chemical and pysical properties of the samples. The results have been compared with insights into building, civilisation and art history of North-East Germany. The results have been saved in a database system.

2. REGISTRATION AND VALUATION BY HISTORY OF ART (ART HISTORICAL

ASSESSMENT)

The registration was necessary to get an overview of the stock of relevant mortars and plasters on medieval churches, of their kinds and volume and their conditions, as well as their special types of ornamental decoration and colouring. Now as ever these valuable fragments of the epidermis of medieval buildings are threated by the environmental pollution, but also ignorance, wrong assessment, inaccurate knowledge of conservation are to blame for important losses. Up to now there have been only few researches concerning the outside of medieval village churches in our region. The reasons for that may be the supposed humbleness of the object. Another reason may be that it is and the impossiblity of the interpreting the findings without cooperation of scientists, restorers and art historians. Thus the project on the one hand led to wellfounded answers to essential questions of technology, age, outer influences and principles of decoration. On the other hand it was possible to form the concrete questions for the natural scientists and to take the probes effectively (acceptable also for conservators). In 1995 there have been two studies of art historical assessment and a systematisation of the findings, we had received through the extensive registration in the counties of Elbe-Elster and Uckermark. The traditional art history with its typological view was completed by the observation of aspects like the treatment of stones, joints, plaster or colouring. So it was possible to create new hypotheses to the medieval organization of building, influences of workshops, clients, economical and political structures. The Usual criterions to determine the age of the buildings have been abroaded. Our picture of the original appearance of the medieval village churches became more more precise.

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In the following there are some facts which were controversial up to now. - stoneworking: It is true, that regular masonry, built with squared field stones, appeares until ca. 1300. Beside them there are also churches, which were built in the same time, but not so accurately, with splitted material. Evidently it depends on the economic strength and the political promotion of the environs. It is possible to demarcate different territories from each other. -mortar-plaster: Correspondent to the usual medieval practise the "squared mason ry" is also in fact erected with two regularly stacked "shells", filled with mortar and smaller, not splitted field stones. This masonry generally was decorated with the double-scratched joint-plaster finally from top to bottom. Thus the mortar is not identical with the joint-plaster and normally we were able to find a "sinter-skin" between. -plaster or no plaster: The accurately squared masonry of the older churches was not covered, only the joints and the edges of the stones were provided with

plaster. Only little areas without square stones

(vaulted parts of the window openings, gable triangels on the east side etc.) were covered with plaster. The later masonry was not so regular, but the aesthetics of the old churches kept obligatory. So the plaster of the later buildings (until the 17th century) has got double scratchings, too, in order to imitate regular masonry.

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1491 -shaping of joints: The regular square masonry corresponded with the "classic" jointshaping: First the smoothed joint plaster was double scratched. Than it became roughed with the trowel beyond the both scratcings. Thus the so created smooth plasterband was in contrast to the rough edges. Later, when the masonry became irregular and the plaster covered the whole stones, the decoration with the plasterband became independent of the real joints and stones. Over the times the net of joints bands became coarser and only double scratched. -colouring: The earlier joint bands had been evidently generally emphasized with chalk. In the Elster-Elbe region are very good examples of special

emphasises of this net by accompanied simple or double red

strokes. Even there are findings of decorations with alternating red-white plaster squares. The emphasis of special architectural details like portals, windows, ledges etc. by decorative scratchings and colouring we have found in the Uckermark, too. Only few colours have been used: white, red and black(gray). 3. SCIENTIFICAL INVESTIGATIONS The targets of the scientifical investigations are: - regional and chronological comparison between the several types of plasters - clearness about the reasons of damages - to find technologies for conservation and restoration. We have investigated the chemical composition of the plasters with the analysis scheme of KNOFEL (1). The mineralogical microfabric has been determined with the light and electron microscop. The sieve lines and the porosities had been also determined. 3.1 Regional and chronological comparison If it was possible we have been determined the plasters of the Middle Ages and the Baroque in the several regions of Brandenburg. We analysed mortars and plasters in the counties Elbe-Elster (southwest of Brandenburg), Uckermark (northeast) and Prignitz (northwest). In same cases the plasters and mortars consist of lime with hydraulic parts, for example in the Prignitz (fig. 3). To use gypsum-binder is not typical. The mixing proportion between binder and aggregats is very high. There was no evidence of significant differences in chemical analyses of mortars and plasters of the involved regions and ages (figure 1-3).

figure 1: Hydraulic contents in the mortars of the county Elbe-Elster

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