Analytical Data for Islamic Ceramics

INTRODUCTION

Some 1200 Islamic pottery sherds from Egypt (Fustat and the Cairo region, Qusier, Aswan), Iran (Susa), Iraq (Samarra, Nineveh, Kish, Hira), and Syria (Ma'arrat al Numan, Queiq, Meskene, Raqqa) spanning the period from the 8th to 14th centuries AD have been analysed using a combination of X-ray fluorescence spectrometry (XRF) operated in air for the glazes, and either atomic absorption spectroscopy (AAS) or proton induced X-ray emission (PIXE) for the bodies (Table 1). The project was directed, and all the glaze analyses undertaken, by the late Alexander Kaczmarczyk. Following on from his previous studies of faience from Egypt and the Near East (Kaczmarczyk and Hedges 1983, Kaczmarczyk 2007), the emphasis of this study has been the analysis of the glaze colorants. Since a high proportion of the pottery is polychrome, several glaze analyses were undertaken for each sherd so that the total number of glaze analyses is some 2600.

For each of the groups of Islamic ceramics listed in Table 1, tables are provided giving glaze data (wt% oxides) grouped by colour together with average compositions for each colour group (Table A); glaze data grouped by sherd (i.e., all analyses for each sherd brought together) together with information on glaze type and body type (where available) for each sherd (Table B); and body compositions (wt% oxides) plus body type for those groups for which these data are available (Table C). A preliminary interpretation of these analytical data in terms of the choice of glaze type, body type and colorants is provided by Tite (in press).

EXPERIMENTAL PROCEDURES

A high proportion of the sherds analysed were provided by the Ashmolean Museum in Oxford and the Musée du Louvre in Paris. In the case of Egypt, Kaczmarczyk also collected sherds from relevant archaeological sites, and in particular, from Fustat near to present day Cairo. In addition, Donald Whitcomb provided a group of sherds from his excavations at Qusier al-Qadim on the Egyptian Red Sea coast. A high proportion of the sherds collected by Kaczmarczyk and those provided from Qusier al-Qadim are available for further study in the Research Laboratory for Archaeology and the History of Art (RLAHA) in Oxford, together with photographs (Table 2).

 

The glaze analyses were made on the glaze surface, or sometimes the glaze edge, using XRF operated in air, and were therefore non-destructive. However, since the analyses were made in air, data were obtained only for elements with atomic number greater than potassium, and therefore, no data are available for the light elements (i.e., sodium, magnesium, aluminium and silicon). On the basis of the different compositions observed for glaze analyses undertaken on a single sherd, the absolute errors ranged from 0.5-3 wt% for oxides present up to about 15 wt%, to 5-10 wt% for oxides present from about 15 wt% upwards. The detection limits varied somewhat from oxide to oxide but were typically about 0.05 wt%.

For the body analyses, which are not available for all the sherds, small samples were drilled from the sides of the sherds, and these were analysed either using AAS in the RLAHA in Oxford, or using PIXE performed with the ALGAE particle accelerator in the Centre de recherche et de restauration des musées de France (C2RMF) based at the Musée du Louvre.

GLAZE TYPES

Since the light elements have not been analysed, the only major glaze components for which there are analytical data are lead oxide, potash and lime. Comparison of the XRF data for those glazes that have also been analysed in polished section in a scanning electron microscope (SEM) using energy dispersive spectrometry (EDS) (Mason and Tite 1997; Mason 2004) indicates reasonable agreement for those oxides (PbO, K2O, CaO, SnO2 and FeO) that were analysed by both methods (Tite, in press). Because the concentration of soda, which is the dominant alkali in Islamic glazes, could not be determined, the different glaze types used are defined entirely on the basis of their lead oxide contents, with the fully quantitative glaze analyses for Islamic glazes (Mason 2004) being used as a guide. Thus, the Islamic glazes were subdivided into the following four types: alkali-lime glazes (<2 wt% PbO), low lead-alkali glazes (2-9.9 wt% PbO), lead-alkali glazes (10-35 wt% PbO), and high lead glazes (>35 wt% PbO).

Each of these glaze types can be further subdivided into transparent and opacified. Other than those colorants that themselves act as opacifiers (i.e., lead antimonate, hematite, chromite), the opacifier used was tin oxide (Mason and Tite 1997). The observed tin oxide contents in the glazes range from less than 0.1 wt% up to about 16 wt% SnO2. However, in the glaze composition tables, tin opacified glazes are defined as those containing greater than 1 wt% SnO2. Although 1 wt% SnO2 is not sufficient to produce an opaque glaze, it is sufficient for some tin oxide to survive as particles within the glaze rather than all being in solution. Also, this concentration is clearly associated with the deliberate addition of tin oxide to the glaze rather than the tin oxide being incorporated as an impurity with, for example, bronze used as the source of the copper colorant.

BODY TYPES

Islamic ceramic bodies are of two primary types; that is, quartz and clay. Quartz or stonepaste bodies comprise typically ten parts quartz sand or crushed quartz, one part glass frit and one part white clay (Mason and Tite 1994). The clay bodies can be further subdivided into calcareous and non-calcareous depending on their lime contents. Thus, the Islamic bodies are made up of the following three types: quartz bodies which contain >75 wt% SiO2, with the great majority >85 wt% SiO2 (typically, <8 wt% Al2O3 and <9 wt% CaO); calcareous clay bodies which contain >6 wt% CaO, with the great majority >10 wt% CaO (typically, >6 wt% Al2O3 with majority >10 wt% Al2O3); and non-calcareous clay bodies which contain, typically, <6 wt% CaO, and >12 wt% Al2O3.

COLOURS AND COLORANTS

The starting point for specifying the colours used in the decoration of the Islamic ceramics are the descriptions and groupings provided by Kaczmarczyk. However, the yellow, green and black colour groups specified by Kaczmarczyk have been subdivided on the basis of the glaze compositions of individual sherds. Thus, the yellow group has been subdivided into those containing antimony, which were coloured and opacified by lead antimonate, and those from which antimony was absent, and which were probably coloured by iron oxide. Similarly the green group has been subdivided into those containing antimony, which were coloured and opacified by a combination of copper oxide and lead antimonate, and those from which antimony was absent. These latter have been further subdivided into those containing less than about 0.5 wt% CuO which were probably partly coloured by iron oxide, and those containing greater than 0.5 wt% CuO which were coloured by copper oxide by itself. Finally, the black group has been subdivided into those coloured by chromium oxide, most probably in the form of chromite particles (FeCr2O4), and those from which chromium was absent, and which were probably coloured by a combination of iron and manganese oxides.

Overall, the glazes are subdivided into the following colour groups:

  • Transparent/translucent
  • White
  • Lustre (including yellow, green, brown and red lustre)
  • Yellow (PbSb) (lead antimonate colorant)
  • Yellow (iron colorant?)
  • Green (PbSb) (copper plus lead antimonate colorant)
  • Green (<0.5 wt% CuO) (iron plus copper colorant)
  • Green (>0.5 wt% CuO) (copper colorant)
  • Turquoise-blue (copper colorant)
  • Dark blue (cobalt colorant)
  • Purple (manganese colorant)
  • Brown (iron plus manganese colorant)
  • Red (hematite colorant?)
  • Black (Fe-Mn) (iron plus manganese colorant)
  • Black (Cr) (chromite colorant)

ACKNOWLEDGEMENTS

The Ashmolean Museum, Oxford and Musée du Louvre, Paris are thanked for the loan of sherds for analysis, and the RLAHA in Oxford and C2RMF in Paris are thanked for providing access to the necessary analytical facilities. The glaze analyses were undertaken using XRF by Alexander Kaczmarczyk at both the RLAHA and the C2RMF. The body analyses were undertaken either using AAS by Helen Hatcher who was working as a Research Assistant at the RLAHA, or using PIXE by Josefina Pérez-Arantegui (currently lecturer at IUCA, University of Zaragoza) who was working as Visiting Research Fellow at the C2RMF.

REFERENCES

Kaczmarczyk, A., 2007, Historical and regional variations in composition, in Faïences et matières vitreuses de l'Orient ancient, (ed. A. Caubet), 29-37, Musée du Louvre, Paris.

Kaczmarczyk, A. and Hedges, R. E. M., 1983, Ancient Egyptian faience: an analytical survey of Egyptian faience from Predynastic to Roman times, Aris and Phillips, Warminster.

Mason, R. B., 2004, Shine like the sun, Royal Ontario Museum, Toronto.

Mason, R. B. and Tite, M. S., 1994, The beginnings of Islamic stonepaste technology, Archaeometry, 36, 77-91.

Mason, R. B. and Tite, M. S., 1997, The beginnings of the tin-opacification of pottery glazes, Archaeometry, 39, 41-58.

Tite, M. S., in press, The technology of glazed Islamic ceramics using data collected by the late Alexander Kaczmarczyk, Archaeometry.

KEY TO DATA PRESENTED IN DATA TABLES (A-C)

The sources of the sherds analysed are as follows:

  • ASH - Ashmolean Museum
  • LOUV - Musée du Louvre
  • ALX - collected by Alexander Kaczmarczyk
  • WHIT - Qusier al-Qadim excavations

The glaze types for the Islamic ceramics are as follows:

  • AL - alkali-lime glazes (PbO <2 wt%)
  • LLA - low lead-alkali glazes (PbO = 2-9.9 wt%)
  • LA - lead-alkali glazes (PbO = 10-35 wt%)
  • HL - high lead glazes (PbO >35 wt%)
  • TO - tin-opacified glazes (SnO2 >1 wt%)

The body types for the Islamic ceramics are as follows:

  • Q - quartz bodies containing >75 wt% SiO2, with the great majority >85 wt% SiO2 (typically, <8 wt% Al2O3 and <9 wt% CaO)
  • CC - calcareous clay bodies containing >6 wt% CaO, with the great majority >10 wt% CaO (typically, >6 wt% Al2O3 with majority >10 wt% Al2O3)
  • NC - non-calcareous clay bodies containing, typically, <6 wt% CaO, and >12 wt% Al2O3

Experimental Procedures

A high proportion of the sherds analysed were provided by the Ashmolean Museum in Oxford and the Musée du Louvre in Paris. In the case of Egypt, Kaczmarczyk also collected sherds from relevant archaeological sites, and in particular, from Fustat near to present day Cairo. In addition, Donald Whitcomb provided a group of sherds from his excavations at Qusier al-Qadim on the Egyptian Red Sea coast.

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Key to Tables

Key to Islamic ceramics tables

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