Siegfried Siegesmund - Monument Future

Figure 5: Results of salt reduction testing using the single poultice samples for a) tombstone I, b) tomstone II and c) tombstone III.

Figure 6: Values of ultrasonic velocity for a) tombstone I, b) tombstone II and c) tombstone III and values of surface hardness for d) tombstone I, e) tombstone II and f) tombstone III before consolidation.

Figure 7: Values of ultrasonic velocity for a) tombstone I, b) tombstone II and c) tombstone III and values of surface hardness for d) tombstone I, e) tombstone II and f) tombstone III after conservation.

Restoration of the tombstones were done using a hot lime reaction mortar (Fig. 8). Similar mortars were already sucessfully prepared for tuffs and sandstones (Teipel et al. 2020, Wedekind et al. 2016b).

The results of the investigations on the objects have shown that, at least in some areas, there is a correlation between the surface hardness measurements and the ultrasonic velocity. In these areas a structural damage can be assumed with low values.

Both values can be positively influenced by consolidation. The intensity of weathering apparently also plays a role here. With heavily softened objects such as tombstone III, the results can be interpreted to mean that the consolidation was only 268partially successful in some areas. If necessary, the amount of consolidant used was not sufficient.

Figure 8: The three tombstones after restoration with the hot lime reaction mortar.

Figure 9: The ultrasonic velocity correlated with the surface hardness of the three tombstones before conservation.

Practical consolidation measures on stone objects can be checked with the presented examination methods. They can provide valuable information on the success or failure of the consolidation method used and are therefore suitable as a control or quality inspection procedure.

The results of the salt reduction showed that there is a clear correlation between the level of electrical conductivity and the intensity of the weathering. This leads to the assumption that salts are primarily responsible for the weathering observed. The intense weathering on tombstone III is probably also due to the high hydric dilatation of the rock material. Clay minerals are probably responsible for the latter, as further investigations should clarify.

We would like to thank Ms. Birgit Busse from the Green Spaces Department of the city of Göttingen for trusting our expertise and for her engaged commitment to the maintenance of the Bartholomew cemetery.

Domaslowski, W. (2003) Preventive conservation of stone historical objects. Torun.

Wedekind, W. (2016 a) Verwitterung und Salzreduzierung von monolithischen Baukörpern aus Sandstein. Vortrag auf der Tagung „Aktuelles aus Forschung und Praxis zum Thema Salz“, Dresden 1.4.2016, doi: 10.5165/hawk-hhg/291.

Wedekind, W., Lopéz-Doncel, R., Ruedrich, J., Siegesmund, S. (2016b) Evaluation of innovative treatments and materials for the conservation of the strongly salt-contaminated Michaelis church in Zeitz, Germany. in: Hughes, J. J., Howind, T. (Eds.) Science and Art: A Future for Stone. Proc. of the 13th Internat. Congress on the Deterioration and Conservation of Stone. Paisley 2016, Volume II, p. 981–990.

Kracke T., Müller C., Krinninger S., Wedekind W., Ruedrich J., Siegesmund S. (2007) Buntsandsteine Göttingens: Verwendung und Verwitterungsverhalten am Beispiel des Bartholomäus Friedhofs. Zeitschrift der Deutschen Gesellschaft für Geowissenschaften (ZDGG), 158/4, 957–984.

Kracke, T., Ruedrich, J., Wedekind, W. Mueller, C., Siegesmund. S. (2008) Weathering Behavior and the Effects of Consolidation Approaches on the Buntsandstein: a Case Study from the Bartholomew Cemetery in Göttingen. In: Jadwiga W. Lukaszewicz & Piotr Niemcewicz (Eds.) Proceedings of the 11th International Congress on Deterioration and Conservation of Stone. 15.–20. September 2008, Torún. Torún 2008, Volume I, p. 677–684.

Teipel, M., Pötzl, Chr., Wedekind, W., Middendorf, B., Siegesmund, S. (2020) Approach on developing stone replacement mortars fort he cultural heritage of Armenia.

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Cristina Tedeschi, Mariagiovanna Taccia

IN: SIEGESMUND, S. & MIDDENDORF, B. (EDS.): MONUMENT FUTURE: DECAY AND CONSERVATION OF STONE.

– PROCEEDINGS OF THE 14TH INTERNATIONAL CONGRESS ON THE DETERIORATION AND CONSERVATION OF STONE –

VOLUME I AND VOLUME II. MITTELDEUTSCHER VERLAG 2020.

Politecnico di Milano, Department of Civil and Environmental Engineering, Italy, cristina.tedeschi@polimi.it

In cultural heritage cleaning techniques are very important and delicate operations, and they are necessary every time the surface of the stone is covered with mostly soiling material to avoid further degradation or alteration. The problem is that often during the cleaning operations, not only the alteration and the degradations are removed, but also part of the materials of the building stones and ornaments, thus damaging it irreversibly.

This paper investigates the effectiveness of 3D optical microscopy, used to monitor the surface of some natural stones, such as Carrara marble, the Noto Limestone and the Serena Stone subjected to mechanical cleaning subjected to mechanical cleaning by micro-sandblasting.

Therefore, we focus on the evaluation of the effects of cleaning on new natural stones taken from the quarry, through 3D mapping and the roughness profile. The selected samples were analysed with the Alicona IF-Portable optical profilometer before and after cleaning to monitor any morphological changes induced on the marble substrate.

In this paper we will analyse the accuracy of 3D optical microscopy to evaluate the impact of a common cleaning technique, called micro-sandblasting.

The cleaning of the stones with a view to preserving cultural heritage is a crucial phase that shows some risks, it is an irreversible process and sometimes can alters the surface and original finishing layer of the building work. There are no real procedures that quantify the degree of cleaning but only a guideline (Mecchi et al. 2008), (Revez, M. J.; Delgado Rodrigues, J., 2016), (Demoulin, T.; et al).