Monument Future

Introduction

Naqsh-e Rustam archeological site is located in Marvdasht municipal territory, in the Fars province, Iran (Figure 1). The site served as a necropolis during the Achaemenian (550–330 BC) and Sassanian (224–651 AD) periods (Schmidt 1970). Naqsh-e Rustam contains the rock-cut tombs of four celebrated kings of ancient Persia, Darius the Great, Xerxes, Artaxerxes, and Darius II.

This paper deals with the conservation issues related to the outstanding bas-relief decorations of these tombs. During the recent years, reports about their progressive decay were repeatedly presented by local conservation experts as well as visitors. Different hypotheses were presented about the causes of threats and decay rates which may be 72put into two main classes. Those which relate the current situation of rock reliefs to the long-term exposure to the open-air weathering processes. On the other hand, it is argued that the rate of decay is drastically increased during the last decade due to anthropic factors such as air pollution, as well as climatic changes such as unexpected seasonal floods and land subsidence.

Due to the difficulties in getting access to the tombs which are located in the upper parts of vertical cliffs, no report, mapping or analytical data was in hand about their previous state of conservation. Therefore, not only a close examination of the stone substance had to be done, but also it was necessary to obtain a clear picture of the state of conservation of the reliefs in the past decades or even longer periods, if possible.

Another specific feature of these reliefs which were dealt with during the previous attempts for conservation in one of the tombs (Darius I) was the uncovering of polychromy. Therefore, it was important to consider the possibility of encountering such features also on other tombs and to discuss their decay problems as well. This study was carried out with the aim to support the decay mapping of rock reliefs, which can be used as a measure for systematic monitoring and mitigation of the risks in the framework of a preventive conservation program in the future. For this reason, a combined methodology consisting of different approaches were applied for data collection about the reliefs. In the meanwhile, it became possible to discover aspects of the original decoration, which was hidden for many years from the experts and visitors.

Research Method

Data were collected for this research through three approaches:

a) Mapping the current situation

b) Collection of historical data for assessing the decay phenomena in a time framework

c) Sampling from representative points and analytical studies for understanding the decay

The bas-reliefs are located at heights between 15 and 38 meters, on the perpendicular rocks. There-fore we inevitably required scaffoldings to gain access to the monuments. The local conservation teams had conventionally used rock climbing equipment under guidance of bouldering professionals for reaching the surface of interest. However, since 2018, scaffoldings have been mounted in front of the tomb of Xerxes, for preforming emergency conservation works.

Figure 1: Map of Iran with the location of the site and rock-cut tomb of Xerxes in Naqsh-e Rustam and its bas-relief decorations.

Close examination was done on the rock reliefs which showed various patterns of decay for the monument. These features were classified using ICOMOS-ISCS glossary on stone decay patterns and UNI 11187:2006 (ICOMOS-ISCS, 2008 & UNI, 2006) based on the mapping methodology developed by Fitzner et al., (1995). The orthophotograph output of laser scanning documentation was used to generate the base map on which the decay features were transported.

In the next step, the decay patterns and their distribution on the surface of rock reliefs were compared with historical resources to assess the changes occurred by the passage of time. The site was one of the main destinations of travelers and scholars since the 17th century. Based on this reality, a search was done for archival material including the site condition in the past. After identification and collection of the historical resources, we focused on any indication of deterioration problems. Not only the graphic sources, such as old photos and drawings, were compared with the decay map, but also, we consider older written materials such as travelers’ accounts with reference to the reliefs. Some of them were analyzed during the 20th century, however, these data were never studied from 73the conservation point of view. For example, the Engelbert Kampfer’s report about the site (1712) was neglected mostly because of the difficulty in translating its specific style of Latin, which was finally partially translated into German in the mid 20th century. However, those parts about Naqsh-e Rustam were put aside. After the completion of these phases, the decay processes were tentatively assessed, on the basis of the collected information, comparing them to the present state of the site, attempting to locate them on the map.

This approach was followed by sampling from representative points on the reliefs. Considering 3 different elevations and the variety of the decay features identified during the mapping process, in total 14 samples were taken from the rock monument.

Two samples were taken from the rock for its characterization. They were taken from the places where detachments had occurred, from the walls due to cracks. Two more samples were taken from the undamaged part of the rock from places more distant from the monument. Other samples were taken from the weathered surface layers (Table 1). Moreover, traces of polychrome decoration on the stone were revealed in the course of emergency conservation operations, which were covered for centuries under layers of soil depositions and crusts. The samples were studied by means of optical and SEM microscopic observations of thin sections and cross-sections, as well as SEM-EDX and XRD analyses. Observations on thin sections and cross-sections of samples were accomplished using a stereomicroscope Leitz Wild M420 at different magnifications and a Scanning electron microscope JEOL 5910 LV, source tungsten filament, coupled with X-ray spectrometer (EDS) in a dispersion of IXRF-2000 energy in order to observe the sequence of the superimposed crusts and samples with traces of polychromy. Analyses were conducted in low vacuum conditions. The compositional nature and distribution of elements on sample was investigated by EDS spectra and maps from 0 to 20 keV. X-ray diffraction was carried out on powdered samples by PANalytical X’Pert PRO X-ray diffractometer, with geometry goniometer θ–θ. The diffractograms were recorded between 3° and 75° 2 θ with a scanning speed of 0.21 θ/sec, using a Cu Kα radiation, a PW generator 3040/60 in the conditions of 40 kV and 40 mA, and a solid-state multi-detector X’Celerator PW3015/20, with Ni filter. Results were interpreted by the use of the X’Pert HighScore software.

In order to give a more comprehensive view to the problem of decay patterns in Naqshe-Rustam, we preferred to focus on one of the main weathering phenomena which predominate the decay patterns in this site and contributes to the progress of other decay problems. We finally discussed one of the specific findings about the remaining traces of surface polychrome decorations, which seem to be very rare and need specific care and conservation measures in the future.

Preliminary Results and Discussions
a) Mapping

Seven types of decay patterns were mainly identified in the close examination of the reliefs (Figure 2).

b) Historical documents

A considerably high number of historical records were identified about the preservation condition of the reliefs. This is due to the fact that the site was very popular among western scholars between 17th and 20th centuries.

Among the identified material, some decay phenomena were described in detail. A critical approach in reading the precedent visitors’ works was especially noted among most of the authors, which make it possible to follow the events through history. According to the first notes written about the site by Pietro Della Valle, the Italian traveler in 17th century (Masetti, 2018) “the very little fragility of the sculptures shows that they are so strong that can last as long as the mountains themselves” (Della Valle, 1843, p. 261). This condition as the beginning point of the survey may be compared with the evidence of decay, which are traced in the early 20th century photos and even the drawings from 18th and 19th centuries. However, it is more 74precise to compare the graphic resources with the present mapped condition. Figure 3 shows examples of specific phenomena, which were discovered.

Figure 2: Example of decay map of the rock reliefs decorations on the façade of Xerxes’s tomb.

c) Laboratory Analysis

The rock substance in Naqshe-Rustam is composed of calcite with little amount of magnesian calcite and even minor phases of quartz (Figure 4). According to the results of mapping activities, the external surface of rock-reliefs is mainly covered by encrustations.

Field observation and also the historical photos showed the link between the movement of water on the stone surface through cracks and fissures in the rock and the formation of crusts. We focus here on this phenomenon and through the results of the analytical approach will discuss the link among it and other forms of decay.

Encrustations are formed as several superimposed layers (with an overall thickness between 0.1 to 0.5 mm). While the intact stone has a color similar to white marble, the crusts color range between dark orange to bright ochres (Figure 5). The SEMEDX analyses showed that these encrustations are composed of Ca, Si, Al, with minor variations.

It was seen in the maps (Figure 2) that a kind of dark coloration is developing as small to medium size patches on the reliefs, especially on the previously encrusted surfaces. This feature is present as a very thin layer, rich in Sulphur, which is formed on the external surface of the overall encrustation. While the older encrustations are basically close to the rock composition with small amounts of aluminum-silicates contamination, the newer phenomenon is connected with a composition of gypsum and bassanite highlighted as minor phases in XRD analyses.

The appearance of crusts in these cases does not change so much (Figure 6). However, the progressive formation of sulphate layers can lead to black crust formation, as an impact of high atmospheric pollution (Fronteau et al., 2010). We still need to complete our studies on the air pollution data for this area.

Figure 3: Comparison between an old photo shot no later than 1939 (Schmidt, 1970) and recent condition of the reliefs, showing the progress of weathering and material loss.

Figure 4: XRD patterns of rock samples of Xerxes’s tomb. Main phases: calcite, minor phases: magnesian calcite.

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Figure 5: Encrustation on the reliefs, (a) Sampling location in the pathway of moisture with crusts of different colors, (b) the polished cross section of crusts, (c) and (d) SEM elemental maps of Si and S for the same sample.

Another secondary decay phenomenon related to the formation of crusts regards the presence of microrganisms. They form a dark film, which is also accompanied by pitting effects (Sohrabi et al., 2017). Microscopic observations showed that this is originally the same encrustation layer which is then contaminated with biological growth. The presence of micro-organisms in the pores of the encrustation layer caused a greyish or darker color. In places near the cracks and fissures conducting the rainwater, it went deeper and caused the detachment of stone pieces from the rock. Therefore, cross sections showed the presence of biologic material not only on the surface layer but also on the opposite side of the sample (Figure 6).

Finally, a very interesting feature was identified in a few samples under the encrustation. SEM/EDX analysis shows a considerable amount of phosphorous in this layer (Figure 7). It is found that this feature is linked to the technique, which was used for polychrome decoration. The first finding of such feature was given nearly two centuries ago by the French archaeologist who discovered traces of blue paint on Darius tomb, under a thick layer of what was described as a calcareous cover, but currently we may classify as a crust layer (Dieulafoy, 1885: 227). There was no report about the polychromy on other tombs of Naqshe-Rustam, especially the Xerxes’s. However, during the conservation activities in the site a few traces of red paint were identified on the rock reliefs, which was given to the authors for analytical studies. We found the same layer with a high amount of P, interpreted as a ground under the paint in those samples.

Similar phosphorous containing material, probably as a product of burning bones, was found in Persepolis, as a ground layer for painting, in constructions attributed to Xerxes era (Ridolfi et al., 2018).

We need to continue the mapping and also to 76compare analytically our findings on Xerxes tomb with the earlier polychromy on the tomb of Darius. Moreover, this discovery enabled us to distinguish the traces of P-rich ground layer of the original polychromy from other superficial depositions on the rock reliefs. This provides an important measure for future conservation works in order to avoid errors such as overcleaning.

Figure 6: Black Biofilm on the reliefs, (a) sampling location, (b) the cross-section of the stone surface with biofilm, (c) and (d) SEM graphs of the surface of same sample showing the biological growth in the porous structure of the crusted surface.

Figure 7: White layer with traces of polychromy on the surface of reliefs, (a) sampling location, (b) cross-section of sample showing traces of red color on the surface with a ground layer between paint and stone, (c) SEM elemental map for Phosphorous.

Conclusions

In this study, it was used a combined methodology including historical archival study and laboratory analysis, in order to identify the decay patterns and evaluate their progress in the course of time, especially during the last 100 years. Moreover, the results of this study uncovered new features about the polychrome layers on the rock reliefs, which can be used in future conservation planning in order to save as much as possible of the historical materials. Analysis of these materials together with recording of their traces and relevant materials on the maps, were carried out for the first time on the tomb of Xerxes. The results showed interesting features about the origins of the phosphorus-containing layer which is in agreement with other evidence of polychromy during the second half of the Achaemenian period.

Acknowledgements

The authors want to thank Dr. H. Fadaei, the head of Persepolis-Pasargadae scientific foundation for supporting this study.

References

Dieulafoy, M. 1885. Mission de Susiane. Note relative à la découverte sur le tombeua de Darius de sept inscriptions nouvelles. Revue Archéologique ser.3.6 : pp. 224–227.

Della Valle, P., 1843, Viaggi di Pietro Della Valle, V. II, Brighton, G. Gancia.

Fitzner B., Heinrichs K. & Kownatzki R., 1995, Weathering formsclassification and mapping, Verwitterungsformen – Klassifizierung und Kartierung. Denkmalpflege und Naturwissenschaft, Natursteinkonservierung 1. Ernst & Sohn, Berlin, pp.41–88.

Fronteau, G., Thomachot-Schneider, C., Chopin, E., Barbin, V., Mouze, D., Pascal, A., 2010. Blackcrust growth and interaction with underlying limestone microfacies. Geological Society, London, Special Publications, 333: 25–34. Kaempfer, E., 1712. Amonitatum exoticarum politico-physico-medicarum fasciculi V, quibus continentur variae relationes, observationes et descriptiones Rerum Persicarum et Ulterioris Asiae. Lemgo. Meyer.

ICOMOS-ISCS, 2008. Illustrated glossary on stone deterioration patterns, English/French version. MONUMENTS AND SITES, XV. Paris: ICOMOS.

Masetti, C., 2018. Città varie e costumi il fin prescrisse. La Persia di Pietro Della Valle (1617–1623). Franco Angeli.

Ridolfi, S., Laurenzi Tabasso, M., Askari Chaverdi, A., Callieri, P., 2018. The Finishing Technique of the Stone Monuments of Persepolis: Further Studies and New Findings Through the Use of Non’Destructive Analytical Techniques. Archeometry, 61(2): pp. 272–281.

Schmidt, E., 1970. Persepolis. Vol. III: The Royal Tombs and Other Monuments. Chicago: Oriental institute.

Sohrabi, M., Favero-Longo, S., Pérez-Ortega, S., Ascaso, C., Haghighat, Z., Talebian, M., Fadaei, H., De los Ríos, A., 2017. Lichen colonization and associated deterioration processes in Pasargadae, UNESCO world heritage site, Iran. International Biodeterioration & Biodegradation, 117: pp. 171–182.

UNI., 2006. 11187:2006 – Beni culturali – Materiali lapidei naturali ed artificiali – Pulitura con tecnologia laser. Milan: UNI – Ente Nazionale Italiano di Unificazione.

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EFFECT OF FIRE ON THE DURABILITY OF A POROUS CALCARENITE: THE CASE STUDY OF A TOBACCO FACTORY IN TRICASE (LECCE, SOUTHERN ITALY)

Emilia Vasanelli¹, Angela Calia¹, Giovanni Quarta¹, Davide Melica², Maurizio Masieri¹, Antonio Monte¹, Francesco Micelli³

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.

1 CNR-ISPC National Research Council – Institute of Science for Cultural Heritage, University Campus, Prov.le Lecce Monteroni, 73100, Lecce, Italy

2 Conservation Scientist via Carlo D’Angiò 31, 73043 Copertino (Lecce), Italy

3 University of Salento Dept. Innovation Engineering University Campus, Prov.le Lecce Monteroni, 73100, Lecce, Italy

Abstract

Thermal decay induced by fire produces chemical and mineralogical alterations, which are often accompanied by discoloration changing the aesthetic characteristics of the stone surfaces. It may compromise also the load-bearing capacity of the masonry elements and lead to stability problems.

Here we report on the investigation of the fire effects on a soft calcarenite used within a masonry building.

Mineralogical transformations of iron hydroxides were detected through XRD and accounted for red discolouring. They were confirmed by DSCTGA analyses and indicated a temperature around 300 °C affecting the stone. Microstructural modifications were investigated by means of optical microscopy and UPV propagation test. A quantitative determination of physical parameters such as color, bulk density, porosity and water uptake was also performed. Implications of thermal stress with the mechanical properties were assessed through uniaxial compressive tests. Thermal effects on the stone microstructure were not microscopically evident. On the contrary, UPV decreases indicated a microfissuring, but this slightly affected porosity, water uptake and compressive strenght.