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Monument Future. Siegfried Siegesmund
Читать онлайн.Название Monument Future
Год выпуска 0
isbn 9783963114229
Автор произведения Siegfried Siegesmund
Жанр Документальная литература
Издательство Автор
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