INVESTIGATION ON ROMAN LEAD GLAZE FROM CANOSA: RESULTS OF CHEMICAL ANALYSES*

Five sherds of green glazed pottery excavated at Canosa (Apulia) in Italy have been analysed by scanning electron microscopy. The aim of the investigation was to determine the chemical composition of the glazes and thus obtain information on the methods used in their production. The glazes were all of the high‐lead type, coloured green by the addition of copper. Intermediate layers, observed at the interface between the glaze and body and giving the appearance of an applied white slip, were the result of the crystallization of lead feldspar from the molten glaze. Non‐calcareous clays were used in the production of the pottery bodies. Concentration profiles from the glaze exterior to the body suggested that the glazes were produced by applying a suspension consisting of lead oxide plus silica to the bodies. On the basis of the glaze and body compositions, it is suggested that the Canosa glazed pottery was produced locally.     

TECHNOLOGY OF PRODUCTION OF GHAZNAVID GLAZED POTTERY FROM BUST AND LASHKAR‐I BAZAR (AFGHANISTAN)

Fifteen fragments of glazed pottery were studied by scanning electron microscopy coupled with energy‐dispersive X‐ray analysis (SEM–EDS). The fragments, dated from between the 11th and the 12th centuries, are part of a group excavated at ancient Bust and Lashkar‐i Bazar (southern Afghanistan) and belonging to the International Museum of Ceramics in Faenza. All the samples are characterized by highly calcareous bodies, and all of them but one is coated with a transparent lead glaze; the last fragment is, instead, coated with a turquoise opaque lead–alkali glaze. With three exceptions, the studied fragments show underglaze decorations featuring white, red, green or black motifs applied on to a white, red or black engobe; one of the remaining glazes is applied on to a monochrome white slip and the other two directly on to the ceramic body. Optical microscopy and SEM images show that engobes and decorations were obtained by deposition of differently coloured clayey slips, the composition of which was characterized by EDS analyses. In particular, black engobes and decorative motifs were obtained by recourse to manganese and iron compounds or to chromium, magnesium and iron compounds; it appears that both possibilities could be exploited for obtaining different decorative motifs on the same object.     

TECHNOLOGY AND COLOUR DEVELOPMENT OF HISPANO-MORESQUE LEAD-GLAZED POTTERY

Lead-glazed pottery from the medieval workshop of Les Olleries Majors (Paterna, Spain) has been studied by Mössbauer spectroscopy, X-ray diffraction, X-ray fluorescence and optical spectroscopy. Yellow, brown and honey-coloured glazes occur on pots glazed on only one surface. They have virtually identical compositions and transmittance spectra, their apparent differences in colour are due to the colours of the underlying pastes. Yellow glazes occur on cream-coloured calcareous bodies, honey-coloured glazes occur on less calcareous bodies with some development of hematite, while brown glazes occur on red siliceous cooking-pots. Green glazes are found on pots glazed on both surfaces; the glazes trapped CO₂ evolved by decomposing carbonates, resulting in an internal reducing environment. This caused the reduction of iron to the ferrous state which coloured the glaze green by diffusion.     

Colouring Agents in the Pottery Glazes of Western Anatolia: New Evidence for the Use of Naples Yellow Pigment Variations During The Late Byzantine Period

A group of the late 12th–13th century Byzantine pottery glazes, mostly related to Zeuxippus Ware Type pottery from the Ku?adas? Kad?kalesi/Anaia site in western Anatolia, was characterized non‐destructively using Raman spectrometry. SEM–EDX was also used complementarily for the glaze characterization. The nature and composition of the glazes, firing conditions, aspects of colour formation and pigments used were discussed. The glazes were found to be lead‐rich silicates, fired close to 700°C on the basis of the Si–O stretching peak maxima of the Raman spectra recorded at ～920–980 cm^–1, as also confirmed by SEM–EDX analysis. The polymerization index values calculated are between approximately 0.05 and 0.1. The use of biscuit‐fired bodies prior to glaze application was suggested based on the results of SEM–EDX analysis. In particular, the detection of Naples yellow pigment variations on a locally produced pottery sample is quite significant, since the use of this type of pigment has hardly ever been reported between the Roman period and the Renaissance.     

The production technology of Iznik pottery—a reassessment*

Previous research has established that Iznik pottery differs from other Islamic stonepaste pottery in that its stonepaste bodies contain lead oxide as well as soda and lime, and that a significant proportion of the tin oxide in its glaze is present in solution rather than as tin oxide particles. In order to better understand these distinguishing features, the chemical compositions and microstructures of Iznik pottery and tile samples, together with those of lumps of glass found in association, were investigated using both scanning electron and optical microscopy. These data have been supplemented by the study of replicate lead–alkali glazes produced in the laboratory with a range of different compositions. The results demonstrate that separate soda–lime and high‐lead glasses were used in the production of Iznik stonepaste bodies, and that the total glass contents of the bodies were significantly higher than those quoted by Abū’l‐Qāsim, who was writing in about ad 1300. The very high purity of the lead–soda Iznik glazes indicated that the alkali flux used was either a purified plant ash or an as yet unidentified mineral source of soda. Replication experiments established that the high solubility of tin oxide in the glaze was due to the high purity of the glaze constituents. Furthermore, it is suggested that tin oxide was added to the glaze in order to give it a very slight opacity and thus obscure any blemishes in the underlying body.     

AN ANALYSIS OF THE GEM‐BLUE GLAZE OF YE WANG'S KOJI POTTERY*

Koji pottery is a glazed ceramic art used widely for figurines. In early Taiwan, it was employed in temple construction for decorative purposes. Ye Wang (1826–87) is the first historically documented Koji artist of Taiwan and also the most prominent Koji pottery artist, noted for his modelling and glazing skills. Unfortunately, his unique technique was lost following his death in 1887. In order to provide vital information for ongoing conservation work on Koji pottery, this study analysed the physical and chemical characteristics of Ye Wang's gem‐blue glaze, to discover the glaze formula. DSC combined with the two‐thirds rule revealed that the firing temperature of Ye Wang's works of art was most probably around 878–923°C. EPMA revealed that the gem‐blue glaze has high alkali levels, and belongs to the PbO–K₂O–B₂O₃–Na₂O–SiO₂ system, deriving its unique colour from copper, iron, manganese and cobalt. This study found high potassium levels in the gem‐blue glaze, which are generally a characteristic of traditional Chinese glazes. In addition, a unique discovery of boron, commonly used in famille rose, was also identified in the glaze. By comparing spectra of historical and reconstructed glazes and adjusting the proportion of chromophoric elements, this study found a glazing formula with colours close to those of Ye Wang's gem‐blue glaze.     

MICRO‐RAMAN SPECTROSCOPY CHARACTERIZATION OF DELLA ROBBIA GLAZES*

Micro‐Raman spectroscopy and the laser‐induced transformation technique were used for systematic study of five coloured glazes on Saint John the Baptist (29 inch tondo), a majolica terracotta relief attributed to Luca Della Robbia and on permanent exhibit in The John and Mable Ringling Museum of Art. We suggest that ions in a lead silicate matrix, called ‘lead ultramarine’, could contribute to the famous Della Robbia blue colour, in addition to the effect of Co atoms as suggested previously by Pappalardo et al. (2004 ). The original yellow glaze contains lead(II) antimonate. The green is a mixture of the yellow and blue pigments, the brown contains hematite, and the white glaze contains tin dioxide as an opacifier. The use of lead oxide as a main fluxing agent is confirmed by laser‐induced micro‐crystallization.     

A Technological Study of the Elamite Polychrome Glazed Bricks at Susa,South‐Western Iran

This study investigated the technological features of the Neo‐Elamite glazed bricks discovered at the Acropolis of Susa, south‐western Iran, by conducting micro‐Raman spectroscopy, differential thermal analysis/thermogravimetry (DTA/TG), X‐ray diffraction (XRD) and scanning electron microscopy–energy‐dispersive X‐ray spectroscopy (SEM–EDS). The results showed that calcium antimonate white and lead antimonate yellow were used as opacifiers in the white, yellow and green glazes, and that green and turquoise glazes were achieved using copper. Coloured glazes were separated by a Si‐rich brown glaze to prevent them from running together during firing. The glazed bricks most probably were not fired at temperatures higher than 900°C.     

CUERDA SECA CERAMICS FROM AL‐ANDALUS,ISLAMIC SPAIN AND PORTUGAL (10TH−12TH CENTURIES AD): INVESTIGATION WITH SEM–EDX AND CATHODOLUMINESCENCE*

Since little is known about the cuerda seca technique, our aim has been to complete an initial analysis of 11th‐century cuerda seca by studying fragments from the 10th century (Pechina, Almería) and the 12th century (Mértola and Almería), so as to establish the diachronic evolution of this technique. Characteristics specific to cuerda seca ceramic glazes were investigated using scanning electron microscopy (SEM) and quantitative chemical analysis with energy‐dispersive X‐ray spectrometry (EDX). The chemical compositions of the different‐coloured glazes (green, black, yellow and white) have given us valuable indications about the evolution of the technique. The opacification mode and the firing process were also investigated. With the help of cathodoluminescence (CL) and the study of modern ‘cuerda seca’ glazed ceramics, new hypotheses regarding the number of firing stages, taking into account glaze and paste transformations and their interactions, are put forward.     

SIENESE ‘ARCHAIC’ MAJOLICA: A TECHNOLOGICAL STUDY OF CERAMIC BODIES AND COATINGS*

The aim of the present study is to reconstruct the production technology of Sienese ‘archaic’ majolica in the early decades of the 14th century ad . The integration of archaeological data with archived data revealed the presence of numerous workshops, suggesting that the Sienese tradition of majolica production was well developed up until the end of the 16th century. Sixty‐seven uncoated and coated waste products were analysed. The ceramic bodies were examined by OM, XRDp, SEM–EDS, XRF, ICP–OES, ICP–MS and INAA. The coatings (enamels and glazes) were analysed by SEM–EDS and Raman microspectroscopy. The results showed that ceramics were rejected due to poor control of the firing temperature (technological wastes), faulty production technology (wastes of uncertain classification) and accidents (post‐firing wastes). Finally, the analyses revealed extreme homogeneity of the ceramic bodies, indicating the continued use of the same raw material over the whole period studied.     

Vietnamese (15th Century) Blue‐And‐White,Tam Thai and Lustre Porcelains/Stonewares: Glaze Composition and Decoration Techniques*

EDS, X‐ray fluorescence, Raman spectroscopy, thermal expansion–shrinkage measurement and scanning electron microscopy were applied to determine the elemental components, structural phases and glazing temperatures of the transparent glazes, blue underglaze and overglaze tam thai (including gold‐like lustre) decorations from the 15th‐century Vietnamese porcelains/stonewares found at the Chu Ðâu–My Xa kiln site and in the Cù Lao Chàm (Hôi An) cargo. The ancient technology for colouring the glazes is discussed. The various blue tones in the underglazed décor result from cobalt‐containing manganese ore, with the intentional addition of iron oxide. The overglaze copper‐green and the gold‐like lustre were obtained by dispersing copper in lead‐based glass. The red colour was made using hematite dispersed in lead‐rich flux.     

Chemical and Textural Characterization of Tin Glazes in Islamic Ceramics from Eastern Spain

Several productions of Islamic tin glazed pottery from eastern Spain have been studied under the chemical and microstructural points of view by means of WDS, SEM/EDX, XRD and XRF analyses. Samples of Islamic pottery from the workshops of Murcia 10th, Zaragoza 11th, Mallorca 11th, Denia 13th, Granada 14th and Córdoba 10th, which represent a wide range of local productions from medieval eastern Spain, have been studied in order to obtain the trends of the technical and compositional evolution. From the experimental data, some common features can be established, as well as some differences. All the Islamic Spanish opaque glazes are lead glazes with PbO contents from 37 to 56%, opacified with tin oxide in the range 4–15%. In all the cases, they were applied on a previously biscuited body made with a Ca-rich clay, probably to produce a buff colour less apparent through the glaze. The thicknesses range from 100 to 150 microns and the opacification is achieved by small crystals of SnO₂(under a micron of size). The main differences are the size and distribution of such small crystals, being smaller in the early Islamic productions (Zaragoza and Murcia) and bigger in the late productions.     

THE BEGINNINGS OF TIN-OPACIFICATION OF POTTERY GLAZES

A multidisciplinary programme of research on the glazed ceramics of the Islamic world has been focused on questions of their dating, provenance and technology. One particular question has been the development of tin-opacified glazes, and the nature of glaze opacification generally in the Islamic world. The findings of the various studies combine to indicate that tin was first used experimentally in Basra, Iraq, in the first half of the eighth century AD, apparently within the context of pre-Islamic opaque-glaze technology. Over the course of the next century, an opaque-glaze technology entirely reliant on tin oxide inclusions was developed in Iraq and Egypt and, subsequently, this technology spread to the rest of the Islamic world and also to Europe.     

DISCOVERY,PRODUCTION AND USE OF TIN‐BASED OPACIFIERS IN GLASSES,ENAMELS AND GLAZES FROM THE LATE IRON AGE ONWARDS: A REASSESSMENT*

Tin‐based opacifiers (lead stannate yellow and tin oxide white) were first used in glass production for a short period in Europe from the second to the first centuries bc , and then again throughout the Roman and Byzantine Empires from the fourth century ad onwards. Tin oxide was also used in the production of Islamic opaque glazes from the ninth century ad , and subsequently in enamels applied to Islamic and Venetian glasses from the 12th century ad onwards. A selection of published analytical data for the tin‐opacified glasses, enamels and glazes is summarized, and the methods used in their production are reassessed. The phase transformations occurring when mixtures of lead oxide, tin oxide and silica are fired are investigated with high temperature X‐ray diffraction (XRD) using a synchrotron radiation source, and these results are used to explain the observed differences in the glass, enamel and glaze compositions. Possible reasons for the use of tin‐based opacifiers in the second to first centuries bc , and for the switch from antimony‐ to tin‐based opacifiers in the fourth century ad are suggested, and the possible contexts in which tin‐based opacifiers might have been discovered are considered. The introduction of tin‐opacified glazes by Islamic potters in the ninth century ad is discussed in terms of technological transfer or independent invention.     

OPTICAL PROPERTIES OF TIN‐OPACIFIED GLAZES*

Tin glazes contain SnO2 particles, with a diameter similar to the wavelength of visible light, which are responsible for glaze opacification. In this paper a theoretical model to explain the optical behaviour of these glazes is developed. This model is tested by measurement of the reflectance and transmittance spectra for different optical paths in Spanish Islamic and mudejar glazed ceramics and it is shown to be valid by total reflectance non‐destructive measurements on a wide range of other Islamic and related glazed ceramics.     

Early Opacifiers In The Glaze Industry Of First Millennium bc Persia: Persepolis And Tepe Rabat

This study characterizes the opacifiers and colouring agents used in the glazed bricks of Persepolis (mid‐first millennium bc ) and the Mannean site of Tepe Rabat in north‐western Iran (eighth to seventh centuries bc ). Various analytical studies show that lead antimonate and brizziite (NaSbO₃) were used as the yellow and white opacifiers in the glazes of Persepolis and Tepe Rabat. Brizziite is shown to be incorporated in the white, green and turquoise glazes, and is also associated with lead antimonate and CaSb₂O₆ in some yellow and white opacifiers. The simultaneous formation of these opacifiers in one glaze might have been accidental. A possible connection between the Achaemenid glaze industry and the Mannean glaze production at Tepe Rabat is discussed.     

LEAD GLAZES IN ANTIQUITY—METHODS OF PRODUCTION AND REASONS FOR USE*

Transparent high lead and tin-opacified lead-alkali glazes have been extensively used throughout Europe and the Near East from their first appearance in the Roman era and the tenth- to eleventh-century Islamic world, respectively, up until the present day. Using, to a large extent, information which is widely scattered through a diverse range of literature, the methods employed in the production of these two glaze types are first outlined and their merits are then compared with those of alkali glazes in terms of ease of preparation of the glaze mixture, ease of application of the glaze, ease of firing, cost of production, glaze-body fit and visual appearance. The principal advantages of transparent high lead glazes as compared to alkali glazes are shown to be ease of preparation and application of the glaze suspension, low susceptibility to glaze ‘crazing’ and ‘crawling’ and high, optical brilliance. Factors that influence the choice of tin-opacified lead-alkali glazes include ease of production of tin oxide by melting tin and lead metals together; a reduced risk of reduction of lead oxide to lead metal and consequent blackening of the glaze; and, again, low susceptibility to ‘crazing’ and ‘crawling’. Limits of current knowledge regarding these two glaze types and requirements for future research are outlined.     

THE EVOLUTION OF LUSTRE CERAMICS FROM MANISES (VALENCIA,SPAIN) BETWEEN THE 14TH AND 18TH CENTURIES

A set of 33 fragments of lustre‐decorated ceramics uncovered during an archaeological excavation in Manises (Valencia, Spain) have been studied. These ceramics were produced in Manises from the 14th to the 18th century. This well‐dated set of ceramic shards represents the diversity of Manises lustre production and is a complete time sequence of reference for the technological analysis. Texture analysis of the glazes has been carried out by SEM–EDAX, the inner and outer surfaces of the lustre decorations being analysed with non‐destructive ion beams by PIXE and RBS, and also by high‐resolution electron microscopy. The results are compared with other lustre productions and the time trend of the microstructures, glaze and lustre composition is analysed. It is concluded that Sn was used to opacify glazes until the beginning of the 17th century and that changes in the lustre microstructure occurred around ad 1500.     

CYPRIOT BYZANTINE GLAZED POTTERY: A STUDY OF THE PAPHOS WORKSHOPS

Twenty‐five samples of Byzantine glazed pottery from two archaeological sites between Limassol and Paphos region (Cyprus), dated between the 12th and 15th century ad were studied using micro X‐ray fluorescence spectroscopy, scanning electron microscopy and X‐ray diffraction analysis. It was found that all the glazes contain lead, following the main manufacturing process of medieval pottery in the Mediterranean territory, while some of them contain tin, possibly for better opacity. Furthermore, it is shown that copper, iron and cobalt with nickel are responsible for the decoration colours. Finally, the application of principal component analysis revealed significant differentiation for some of the samples.     

LEAD ISOTOPE ANALYSES OF ISLAMIC POTTERY GLAZES FROM FUSTAT,EGYPT*

Lead isotope analyses have been undertaken on a group of Islamic lead‐glazed pottery artefacts from Fustat, Egypt, spanning the period from the eighth to the 14th century ad , that had previously been the subject of a comprehensive typological, chronological, petrographic and technological study. Comparison of the lead isotope ratios for the glazes with those for lead ores from Egypt, Iran, Tunisia, Anatolia, Greece, Sardinia and Spain provided information on the possible sources of the lead used in the production of the glazes. The results show that the lead used in glaze production by the Islamic potters at Fustat was most probably obtained from distant ore sources in Iran or Tunisia, Sardinia, Spain and the Taurus Mountains. Different ore sources were favoured in different periods and, to a limited extent, for different types of pottery, but at no time did the Fustat potters use the potentially more accessible Egyptian ore sources.