Investigation of gypsum-based historical materials has two main problems: philological problems and technical issues. Technical issues, the main topic of this article, are normally consequences of physicochemical complexity of gypsum crystals in different conditions and variety of additives or mixed materials. Neglecting this technical problem, leads researchers to misunderstand or misinterpret these materials. Moreover, exclusively use of one analytical method, such as scanning electron microscope or X-ray fluorescence, provides an incomplete picture of samples that regularly produces further misunderstanding of specimen or its history. The methodology of this study is a multianalytical approach via XRD, SEM and using image analysis software on electron photomicrographs to estimate amount of free spaces in microstructure of samples. A group of three experimental samples were made from traditional recipes of craftsmen in Iran, in order to make a connection between philological problems came from tradition, and technical problems came from mineralogical property of gypsum. Gach-e Tiz, or quick setting mortar shows a very dense microstructure in SEM micrographs. Variety sizes of monoclinic crystals of gypsum are present in it, and moreover some shapeless and bulky regions are also visible. Gach-e Kam-Mayeh, or low setting mortar reveals a much more open microstructure than the former one, filled with needle like crystals and a lot of micro porosity between crystals. There is no evidence of bulky forms area in Gach-e Kam-Mayeh. Gach-e Koshteh, or mechanical low-setting mortar which is a traditional Iranian recipe, shows a parallel layers of laminar gypsum crystals setting upon each other. This form also demonstrates no evidence of bulky regions. Historical samples were collected from a stucco decoration belong to Kuh-e Khwaja of Sistan; a gypsum mortar fragment from Shadyakh, Neyshabur and a piece of gypsum mortar from Alamut castle of Qazvin. The results of XRD show that both layers of Kuh-e Khwaja stucco contain anhydrite as the major phase and the sample of Shadiyakh mostly composed of Gypsum. Organic materials extractions represent no evidence of organic additive to this historical materials. Therefore the images of their microstructure are comparable with experimental samples that made without any additive. Lower layer of Kuh-e Khwaja's stucco shows a lot of tiny crystals that are not very look like gypsum, but precipitated on the surface of bigger and deformed crystals. The microstructure of it is very open and include big amount of micro porosity in compare with other samples. Upper layer of this stucco shows not any form of gypsum crystals but very disturbed flaked shapes, supposedly gypsum crystals transformed to anhydrate. The micrographs of Shadiyakh's mortar also reveal not any clear form of gypsum crystals but base on XRD result it still as gypsum materials. This sample contains mostly from that bulky and dense structure which shows the usage of low amount of water for its paste. The results of image an...

No abstract

No abstract

No abstract

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 (μ-XRF), scanning electron microscopy (SEM), 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 Qazvin, 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.