Technological study of the seventeenth century haft rang tiles in Iran with a comparative view to the cuerda seca tiles in Spain.

Parviz Holakooei

Abstract


The history of polychrome glazed objects in Iran is synchronised with the history of the first known examples of polychrome glazed artifacts. The polychrome glazed bricks of Chughā Zanbīl, dated back to the thirteenth century BC, might be the first evidences of such a claim. This tradition was followed until the fall of the Achaemenids in the fourth century BC, when glazed bricks objects were vastly used to cover the friezes of palaces and important edifices at Persepolis and Susa. Making polychrome glazes on ceramic materials, however, seems to be abandoned until the Islamic period, when polychrome underglaze objects were widely in use in Iran from the tenth century onwards. The first evidences of creating overglaze polychrome decoration was nevertheless achieved on mīnāʾī glazed objects in the thirteenth century AD, which as Abu’l Qasim stated used be originally called haft rang, e.g. ‘seven colours.’ This technique was slightly modified and used throughout the fifteenth and sixteen centuries in Iran, and then was extensively used in the seventeenth century over the Safavid period (1501-1736). In all these types of polychromies, a dark colour line (mostly black) is used to separate various coloured glazes. This technique is still alive and is widely used in decorating the architectural facades of scholastic buildings in Iran. In the twentieth century, art historians attributed this type of polychrome technique to a Spanish style of making polychrome glazed objects called cuerda seca. The only feature by which such an attribution is established is a ‘black line,’ which is used in both techniques of haft rang and cuerda seca for separating coloured glazes. This thesis provides firsthand information about the seventeenth century haft rang tiles in Iran using various analytical approaches, including optical microscopy, wavelength dispersive x-ray fluorescence (WDXRF), x-ray diffraction (XRD), densitometry, ultraviolet visible spectroscopy (UV-Vis spectroscopy), micro-Raman spectroscopy, and energy dispersive x-ray spectroscopy (EDS). Here, optical microscopy was mainly used to have a general idea about the stratigraphy and various layers of the haft rang tiles. WDXRF was however used to respond to the question of the provenance of the tiles as this subject has always been of interest to frame the archaeological context of haft rang tiles. Another issue emphasised in this thesis is the thermal history of the tiles, which was studied by XRD and measuring the density of the bodies’ tiles. This subject was particularly was interesting for me to delve into because multi layer structure of haft rang tiles makes the study of thermal behaviour of the bodies much complicated. On the other hand, the study of the coloured glazes was firstly achieved by UV-Vis spectroscopy, where the possible colourants and network modifiers of the glazes were studied. Micro- Raman spectroscopy, however, presented very notable results about the opacifiers and un-dissolved particles suspended in the glazes’ matrixes. EDS microanalyses were nonetheless carried out to have a general idea about the chemical composition of the glazes and their fluxes, opacifiers, and network formers. ii The results of the aforementioned studies showed that, regardless where they are found, the bodies of the seventeenth century haft rang tiles are local products and are not imported from other centres of tilemaking. Moreover, under the optical microscope three layers of a terracotta body, a white glaze, and coloured glazes could be observed in a single haft rang tile from the bottom up to the top of the tile. In addition, the thermal history of the tiles’ bodies showed that the tiles were not fired most probably at temperatures higher than 1000°C. In fact, the equivalent firing temperature (EFT) of the majority of these tiles was estimated to be between 800 and 1000°C. As far as the white glaze is concerned, it was achieved by dispersing tin oxide particle in an alkali glaze as opacifier. The lead content of the white glazes can be technically associated with the manufacturing white glazes in medieval Iran, where tin and lead was roasted to make an opacifier for alkali glazes. Another issue concerning the white glaze was its maturing temperature, which was estimated to be at about 850°C. The yellow glazes were however achieved by dispersing lead tin yellow particles in a lead-based glaze. The green and brown glazes were practically the yellow glazes in which copper(II) and iron(III) respectively used. The maturing temperature of the yellow, green, and brown glazes was calculated to be roughly placed at 615°C. The blue, violet, and turquoise glazes showed however different behaviour by an alkali matrix in which cobalt(II), manganese(III), and copper(II) had yielded the blue, violet, and turquoise tones. The maturing temperature of these glazes was assessed to be at about 700°C. The black lines did not show to be true glazes due to the high alumina and manganese oxide contents in their composition. The high maturing temperature of about 1150°C of the black glazes revealed very interesting results. This property has certainly been of interest in manufacturing haft rang tiles; that is, when the low temperature glazes were runny enough to be mixed together, the black line was resistant enough to keep separated the glazes in order not to run together. The relatively higher maturing temperature of the white glaze has also been desirable since it does not softened in low temperatures at which the upper coloured glazes were runny and the chance of mixing the white glaze and the upper glazes was substantially lessened. Another subject on which this thesis shed light is the attribution of haft rang technique to the Spanish technique of cuerda seca. In the discussion and final chapters of the thesis, an attempt is made to put together the technological features of these two techniques. What can be at least understood on the evidences exist about these two techniques is that there is no technological reason by which haft rang technique can be attributed to cuerda seca. The use of black line for separating coloured glazes in Iran, as showed in this thesis, has a history much longer the history of cuerda seca. Hence, I have finally suggested that cuerda seca is an inappropriate term to cover the seventeenth century Persian polychrome tiles. The term ‘haft rang,’ which is used for nominating the antecedents of the seventeenth century polychrome tiles, is preferred in this thesis as this term is also widely used in today’s Iran to address this type of polychrome tiles. Parviz Holakooei Ferrara, Italy March 2013

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ISSN: 1974-918X