Historical and Technological Studies of the Khwarazmshahid Brickwork and Glazed Decorations in Khorasan (North-Eastern of Iran)

The Khorāsān, a vast territory covering northern Afghanistan, north-eastern Iran and some parts of Central Asia, now is limited to a region in the north-eastern modern Iran divided into three provinces; i.e., Razavi Khorāsān, North Khorāsān and South Khorāsān. From the last quarter of the twelfth century to the first quarter of the thirteenth century, this territory was in the hands of Khwārazmshāhids in a short interval between the Seljuk and Mongol periods. The history of the Khwārazmshāhids began with the Anush Tigin reign in 1077 AD and declined in 1220 AD by the Mongol conquest, and at the summit of this period their land stretched from the Zagros Mountains (west of Iran) to the borders of India. During the Khwārazmshāhid period, several important buildings were erected of which six have been survived in Khorasan; i.e., the Masjed-e Jāmeʿ-e Gonābād, the Zuzan mosque, the Farumad Mosque, the Masjed-e Jāmeʿ-e Sangān-e Pāʾin, the Masjed-e Jāmeʿ-e Ferdows and the Khosrowshir mosque. The Masjed-e Jāmeʿ-e Gonābād (1212 AD) and the Zuzan mosque show a typical style of this period; the two-iwan plan that these mosques are based on, and brickwork combined with insets glazed ornaments to cover the facades. Accordingly, the Farumad Mosque, the Masjed-e Jāmeʿ-e Sangān-e Pāʾin, the Masjed-e Jāmeʿ-e Ferdows and the Khosrowshir mosque can be built or decorated in the Khwārazmshāhid period. The results obtained from on site investigations showed that the arranged, borida and tarāshida (forming the brick-based elements to create the patterns by cutting and carving the normal fired brick respectively) are the techniques widely used in the pre-Khwārazmshāhid buildings. The pish-shekli (forming the wet brick paste by cutting, engraving, moulding, etc. before any firing treatment) is another technique for producing brick-based ornaments before the Khwārazmshāhids. Besides, engraving the surface of plain brick courses, the so-called pas-tarāshida technique, is also employed to create the decorative patterns at a few monuments before and contemporary with the Khwārazmshāhid period beyond the Khorāsān's frontiers. As far as the architectural decorations of above-mentioned monuments are concerned, the pish-shekli and borida bricks are mainly used to decoratethe Masjed-e Jāmeʿ-e Gonābād while borida and tarāshida bricks decorate the façades of the madrasa/mosque of Zuzan where the found pish-shekli elements are attributed to its destroyed pre-Khwārazmshāhid buildings. The glazed ornaments of the Masjed-e Jāmeʿ-e Gonābād (hobnail and small triangular pieces) are turquoise in colour although turquoise, blue-dark and white glazes with different shapes are used to decorate the façades of the Zuzan mosque. In addition, brickwork combined with glazed elements decorates the undated above-mentioned monuments. The majority of the brick-based embellishments at the Masjed-e Jāmeʿ-e Ferdows and Masjed-e Jāmeʿ-e Sangān-e Pāʾin are pish-shekli elements with different shapes, sizes and motifs combined with glazed ornaments. The pish-shekli bricks at the Masjed-e Jāmeʿ-e Ferdows contain geometric patterns and the triangular turquoise glazed pieces are cut from an older inscription. In the contrary, the pish-shekli bricks at the Masjed-e Jāmeʿ-e Sangān-e Pāʾin are composed of floral patterns (with less frequent geometric patterns and epigraphy) with special shapes. The glazed ornaments of this mosque are some circular elements on which the word al-Molk is applied. On the other hand, the brickwork in the mosque of Farumad are executed in moulded and stamped pish-shekli elements with geometric and floral patterns however there are two friezes with carved pish-shekli elements in this monument. Insets with glazed ornaments (turquoise and less frequent dark-blue, lustre and underglazed painted) are occasionally employed to decorate the façades of the courtyard of the Farumad mosque. Moreover, in the semi-ruined mosque of Khosrowshir, beside the moulded and stamped brick-based decorations, similar to those at the Farumad mosque, the carved pish-shekli and tarāshida bricks are also employed. Likewise, two glazed architectural decorations were found in the surface survey around this mosque. Analytical studies took another important part of studies performed on the brickwork and glazed ornaments of the above-mentioned monuments. More than hundred samples, including brickwork decorations, glazed elements, structural bricks and glaze together with local clays were collected were subject of various analytical methods such as wavelength dispersive X-ray fluorescence spectrometry (WDXRF) and inductively coupled plasma mass spectrometry (ICP-MS). Besides, micro-Raman spectroscopy (μ-Raman), micro X-ray fluorescence (μ-XRF), scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX) and thin section petrography were used to respond to the occasional technological questions. Principal component analysis (PCA) was also used to handle the compositional data of the bodies and glazes. Handling the data obtained by WDXRF by PCA, the bodies were classfied into two main categories in terms of the SiO2 concentration; that is, clay bodies and stone-paste bodies. Accordingly, beside the clay-based brickwork, the glazed decorations of the mosques of Gonābād, Ferdows and Khosrowshir were made on stone-paste bodies while those of the Zuzan mosque were applied on both clay-based and stone-paste bodies. Moreover, the results showed that the chemical composition of the samples of the Gonābād, Khosrowshir and Zuzan were different while the Ferdows’ samples were grouped with those of the Zuzan mosque. Moreover, statistically handling the WDXRF data on the clay bodies, it was proved that most of clay bodies were made of local clays except the samples of the Zuzan mosque. Furthermore, WDXRF, performed on the clay-bodies, showed that most of the samples of the Farumad mosque, with three exceptions, were grouped in a separate cluster. A strong correlation of Mg and Cr accounted for the clay bodies of the Farumad mosque showed that the clay used in the bodies was most probably supplied from the local clay sources near Farumad. Concerning the glazes, cross sections of the glazed bodies under polarised light microscope showed a priming white layer between bodies and glazes in most of the stone-paste samples. Moreover, the ICP-MS results suggested that cobalt and copper were the main colouring agents of the glazes which are responsible for dark-blue and turquoise colours respectively. Handling the ICP-MS data by PCA, it was shown that all the glazes were basically alkali in nature to which Pb and Sn were added to opacify some glazes. The reddish (or buff) colour of the clay bodies was, in fact, covered with tin-opacified glazes to cover the reddish colour of the bodies although opacified glazes were occasionally observed on stone-paste bodies