Technological study of the gilded haft-rang tiles of the Imamzadih Ismail mausoleum in Qazvin, Iran

Background: Gilding decorations on Islamic tiles have been previously studied either historically or technologically. The major emphasis in these studies has always been focused on the use of gold leaf on glazed tiles. The current research has been conducted by electron probe micro analysis (EPMA), portable micro X-ray fluorescence (mu-XRF), scanning electron microscopy (SEMI), optical microscopy and atomic force microscopy (AFM) to shed light on a less known technique of gilding applied on the nineteenth century haft rang glazed tiles of the Imamzadih Ismail mausoleum in Qazyin, Iran. Results: Our observations showed that the gilding decorations are performed on a blue alkali glaze. Plant ash was suggested to be the source of alkali and cobalt was identified as the colouring agent of the glaze. Moreover, trace amounts of arsenic in the composition of the blue glaze was interpreted to be associated with the colouring agent of the glaze; i.e., cobalt. Furthermore, the gilding decorations were suggested to be achieved by firing gold powder on the pre-fired blue substrate glaze. AFM, SEM and optical microscopy proved that the gold flakes partially penetrated the pre-fired blue substrate glaze. Conclusions: This paper established a local provenance for the colouring agent of the blue glaze used as a substrate of gilding decorations. In addition, our studies showed that the gilding decorations were achieved by firing gold powder on the pre-fired blue glaze of a nineteenth century Persian haft rang tile.