Study and Recognition of Mineral Matter of Pastiglia Layer and Gliding of Safavid Period in Qazvin Chehelsotoun

The wall paintings of Qazvin Chehelsotoun Mansion include two periods in the early Safavid period and one period in the Qajar period. This topic has received little attention in the field of structural studies and stylistics. Investigating these decorations in order to understand the evolution of this art and considering the temporal precedence over other murals in the Safavid period seems necessary. (Especially in Isfahan) The main question of this research is to identify the structure and examine the differences and similarities between the techniques of layering and gilding in different layers related to the Safavid era in this monument. The research hypothesis is based on the similarity of materials and techniques used in the two short and successive time periods. The purpose of the study is to identify possible differences in the structure of the materials and techniques of layering and gilding in these two eras of the Chehelsotoun monument. For the reasons mentioned above, the western part of the south corridor and the motif patterns associated with these two periods were selected.  Dental instruments were used for sampling to the depth of the plaster bed layer.    After microscopic examination and coding of the samples, two specimens were selected to study the motif layers of both periods from the upper to the lower substrate.
To identify the elements and ingredients of these motifs, the microscopic images were examined by SEM-EDX microscope.
In order to identify and detect the composition of materials in different phases, different decorative and gilding layers (gold layer, red soil layer and plaster substrate) were examined by XRD imaging.
The results of this research show that the techniques of layering and gilding are identical in these two periods. There is only a slight difference in the purity of the gold and plaster substrates used during these periods.  The gold used in the first period has metallic impurities and its gypsum substrate contains the anhydrite phase which is not seen in the second period. The results can be useful in studying the art of mural painting. These findings can be used for further studies regarding the recognition of clamps and preservatives material used in building decoration.
Keywords: SEM-EDS, XRD, Pastiglia, Gilding, Qazvin Chehelsotoun.
 
Introduction
The city of Qazvin is located in the northern part of Iran and west of its capital. Qazvin has been the capital city of Iran for more than half a century in the Safavid era.
Today only a few important monuments of that era remained. That is why they all need special attention to identify, maintain and introduce.
  Among these monuments, the Chehelsotoun mansion is very important because of the remaining of the early Safavid murals.
 For this reason, this monument and its decorations require extensive research (Figure 1).
Wall paintings are among the decorative arts used in architecture that incorporate any type of paintings with layers of color.
 Based on the quality of the work, this art consists of at least two layers, including of support (architectural structure) and color layer (motifs) and can extended up to six layers.   These layers are: supporter, primer layer, bedding layer, canvas painting layer, color layer and protective or varnish layer (Hamzavi, 2016).
Wall decorations of Qazvin Chehelsotoun mansion have been created in three time periods. These include two periods in the early Safavid kingdom and one in the Qajar period. (Probably during the reign of Saad al-Saltanah)
Many scholars believe that the first layer of wall paintings and ornaments of the Chehelsotoun was built during the reign of Shah Tahmasb Safavid. (Mashrouteh, 2012: 75;  Monshi e Qomi, 1987)
The second layer of these decorations seems to be from the time of Shah Abbas Safavi. (Parhizgari, 2012: 489).
The question of this study is to identify and investigate the differences and similarities between the layered arrays and the gilding of the Safavid era and The hypothesis of this study is that, the techniques of work execution in these two periods are similar. Of course, differences in the style of the mural of these two periods can be seen due to the change in artists and their styles.
 These differences can be identified by studying the style of the murals.  The purpose of this study is not to investigate the style of the motifs. Rather, structural recognition and consideration of possible variables in the technique of placing the layers and gilded in those two periods are considered.
 
Results and Findings of the Research
In studies with Digital Loupe on samples from both periods, three layers were identified.  These layers, respectively, from outer to inner part are: gold layer, red layer and white substrate
To the naked eye, these layers are also visible in the fracture sections of the monuments. On some samples, parts of the red layer are thicker, which makes that parts of painting thicker than others. Also, in some samples there are two layers of white (plaster) of varying thickness, the lower layer being relatively darker and probably is the lining base (Figure 3).
 
Conclusion
Examination of the arrays of layers during the two Safavid eras in Qazvin Chehelston monument shows the same execution techniques and materials used.
Both periods of this ornamentation, depending on the minerals used, include gypsum substrate, red soil layer and gold sheets. The differences between the layers of these two periods are also quite minor, depending on the purity of the gold and plaster sheets used in the bed.
In the first period, copper (Cu), zinc (Zn) and slightly tin (Sn) metal impurities are present in the gold layer (X.1.1), which is absent in the second period of the gold layer decorations (X.2.1).
This may be related to the political and economic conditions of governments. This difference can be traced back to extensive studies of the quality of materials used in different historical periods and to compare them together.
In the base layer and the first period bed (X.1.3), anhydrite mineralization with gypsum was detected which is not seen in the second period bedding (X.2.3).
Investigating this issue requires a case study of its cause. This change reflects the high temperature of the gypsum baking or presence of salts.
The results of this study can be compared with other similar studies on Safavid murals.
The hypothesis of this study is also confirmed that the paintings of the two Safavid periods in Qazvin Chehelston monument are the same in terms of technique of execution according to the near time periods.  These paintings can only be different in style. However, this requires further research.
In general, the process of human handicrafts changes when supply does not meet the political, economic, social and cultural needs.
These changes usually take place over a long period of time and are achieved in short periods of time by revolutionary transformations such as warfare or the discovery and development of more efficient techniques.
As a result, two different periods of Safavid paintings on the Qazvin Chehelston monument took place on the same path and for a short period of time and could reasonably have the same principles.
The existence of the second layer in the building can be primarily attributed to the renovation and reconstruction of the building, which still retains its importance and use in the second period.  Secondly, this may have been due to the adaption of decorations with the current art style in the new era.
On the other hand, because of the importance of gold in human societies throughout history, the purity of the gold sheets used in the second period may indicate a stabilized and better political and economic situation than the previous period.
The result of this research can be studied more thoroughly by further investigations on murals belonging to different eras of Qazvin Chehelston monument as well as decorations to the rest of the related monuments.
Finally, it is necessary to explain that in this research, the study of organic materials used as fasteners for gold sheets has not been performed.  This study is recommended for future research.