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Hamzavi Y, Koochakzaei A, Negarestani A. (2021). Characterization of Colored Mortar of Boumsab Gypsum Arrays of Ganjali Khan School (Caravanserai) in Kerman. Parseh J. Archaeol. Stud.. 5(17), : 14 doi:10.30699/PJAS.5.17.287
URL: http://journal.richt.ir/mbp/article-1-497-en.html

Abstract
Ganjali Khan School (Caravanserai) in Kerman is one of the prominent buildings in Kerman from the Safavid period. Valuable gypsum arrays with different techniques have been implemented in this building. Among these arrays there are the Boumsab gypsum arrays that are executed in the royal room on all sides as well as the roof of the building. One of the special features of these arrays is the color of the mortar in the layers of the lower fine coat and the upper fine coat, which can be seen in three colors: red, yellow and gray. It should be noted that in the past, a layer of gypsum plaster has been applied on the surface of gypsum arrays in this building, but fortunately, in recent years, a large part of the additional layer has been peeled off the surface of gypsum arrays. Due to being special of this architectural arrangement and have not been done any detailed scientific study on these works so far, in this article, the structure of the colored mortars of this building has been investigated. Some of the questions of this research are: What is the structure of the colored mortars of Boumsab gypsum arrays in this building? What are the Major and Minor phases of mortar composition? What was the pigment in colored mortars? In this regard, sampling was done and FTIR, EDS, XRD analyzes were performed, which along with field studies, the research questions are answered. The results of the research show that gypsum mortar with the Major phases of gypsum and anhydrite has been used in different layers. Iron oxide (goethite) was also used to color the red and yellow mortars, and ash and lime were used for the gray mortar. Also, organic materials that used to change the quality of mortar were not identified in the structure of the samples.
Keywords: Gypsum Arrays, Colored Mortar, FTIR, EDS, XRD.

Introduction
Boumsab gypsum array is one of the types of low-rise architectural arrays. In this method, abrasion of areas from the fine coat (Intonaco) surface is done in order to create a different texture between the patterns and the background, the abrasion action covers only a part of the thickness of the fine coat layer and does not reach the layers under the fine coat. This method of stucco has been common in Isfahan since the time of Shah Abbas I (Aslani, 1391: 136). Ganjali Khan School (Caravanserai) in Kerman is one of the Monument in which the high quality Boumsab gypsum array has been executed. This Monument was built at the same time as the Ganjali Khan complex in the Safavid period, and one of the most beautiful architectural spaces in terms of architectural layout is the royal room, which is decorated with a gypsum arrangement of Boumsab. One of the features of the Boumsab gypsum array in this building that makes this array one of the other Boumsab gypsum arrays that have been identified as a result of the authors’ field studies (Aliqapoo in Isfahan, Pirnia House in Nain, Aliqapoo in Qazvin, and Kalkhoran Tomb in Ardabil), is the use of colored mortar in the fine coat layers performed in the royal school of Ganjali Khan School in Kerman. In this Monument, three colors of mortar are gray, red and yellow. Due to the fact that two layers of colored substrate are used on all sides as well as the ceiling of the room, at first it seems that gypsum mosaic is of Tokhmedaravari type, but by studying it closely, it can be concluded that Bumsab gypsum array. Another point is that the Boumsab gypsum array with these properties and with three colored mortars in one space, has been studied for the first time in Iran. 

Result and Discussion
FT-IR: In the spectrum of sample R-1 (Figure 5), the index vibrations of the gypsum can be seen in 3543, 1621, 1114, 670 and 600 cm-1 (Knittle et al., 2001: 635). However, there is a noticeable structural difference in this sample compared to the western side samples. In the spectrum of this sample, absorption bands of about 713, 874, 1430, 1800 and 2516 cm-1 are observed, which are related to carbonate vibrations in the calcite structure (Ylmen & Jaglid, 2013: 121). However, in addition to the absorption bands mentioned, bands of about 469, 521 (Fe-O), 795, and about 3650 cm-1 can be seen next to the 3543 cm-1 gypsum band. These absorption bands are generally visible in the red color spectrum of iron oxides. According to the researchers, these absorption bands and their position increase the possibility of using Hormoz bole or Armenian bole in this sample (ulaiuladienė et al., 2018: 249). 
EDS: The results of EDS analysis of the samples are presented in Table 1. For the amount of sulfur obtained from the S-2 sample in this study 13.02, the amount of 16.27% calcium is required for the gypsum composition. As can be seen in Table 2, the amount of calcium is greater than the amount required for the gypsum composition. 1.7% of the excess calcium can be related to the impurity of lime in the sample, which is normal in historical monuments. Examination of samples R-1, R-2 and R-3 show a significant amount of iron. Therefore, the results indicate the possibility of using iron compounds (ochre) as a red pigment in these samples.
XRD: Two samples R-1 and R-2 were examined using XRD, the results of which are presented in Table 3 and Figure 6. The main phases of R-1 are gypsum and anhydrite, and the sub-phases are quartz, kaolinite and goethite. The R-2 sample is similar to the R-1 sample in terms of the obtained phases, except that kaolinite is one of the main phases. Usually the scratch coat (Arriccio) has added soil and sometimes ash. A small amount of goethite seems to be sufficient to create a red color in the gypsum mortar. The study of the constituent phases of the G-1 sample structure was also performed using XRD, of which gypsum and anhydrite are the main phases and quartz and kaolinite are its sub-phases.

Conclusion
In this study, sampling was performed from different layers of colored mortar and specialized studies were performed. As a result of FT-IR, it can be said that the mortar of fine coat layers are made of gypsum with low lime impurity to which some red pigment has been added at the time of curing to make the mortar red. Also, no evidence of organic matter as additives to gypsum mortar was identified. The results of EDS analysis on gypsum mortar showed the presence of a small amount of excess calcium. Also, in the red mortars of the Bottom and top fine coat layers, iron was identified as the coloring agent and the presence of red was recently confirmed. In gray mortar, the presence of ash mixed with lime is a strong possibility. XRD analysis of four selected samples showed that the predominant phase in all four cases was gypsum and anhydrite, and only in one of the samples, kaolinite was identified as the main phase. The identified sub-phases are quartz, kaolinite and goethite. So far, no research has been published on the composition of Boumsab gypsum plaster with colored mortar. It can be imagined that at first, in order to implement the gypsum array for Tokhmehdaravari, Bottom and top fine coat layers were both applied with colored mortar, and for some reason (for which we don’t know) the decision was changed. Finally, the designs are executed only on the surface layer and And has been executed in a Boumsab manner. It is noteworthy that in the same complex (in the royal porch), a Tokhmehdaravari has been executed and can be seen at present.