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.     

High‐boron and High‐alumina Middle Byzantine (10th–12th Century ce) Glass Bracelets: A Western Anatolian Glass Industry

The trace element boron is present in most ancient glasses as an impurity, and high boron (≥ 300 ppm) marks raw material sources that are geologically specific and relatively uncommon. Recent analyses of Byzantine glass with high boron contents suggest that glass‐making was not limited to the traditional regions of the Levant and Egypt, and a production origin in or near western Anatolia is proposed. Glass bracelets from ?i?n al‐Tīnāt in southern Turkey give fresh evidence for the production and circulation of high‐boron glasses that closely correlates with object typology. The patterning of findspots suggests that high‐boron glass was closely connected to the Byzantine world.     

Glass Beads from 15th–17th Century CE Jar Burial Sites in Cambodia's Cardamom Mountains

A total of 74 glass beads, included as grave goods in 15th–17th century CE jar burials from Cambodia's Cardamom Mountains, were analysed using laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS). Several glass types were identified, including two subtypes of high‐alumina mineral soda glass, and lead–potash glass. The final glass type represents a newly discovered and previously unidentified type of high‐alumina soda glass, with high magnesia (m‐Na–Al Mg>). This study represents the first glass data from the mid‐second millennium CE from Cambodia and sheds light on the multiple long‐distance maritime exchange networks in which the upland people buried in the jars were participating.     

Potassium–Calcium Glass: New Data and Experiments*

The chemical composition of potassium–calcium ‘wood‐ash’ glass reflects the elemental pattern of the involved non‐volatile base materials in quartz sand, wood ash and possibly potash. The essential elemental ratio K₂O/CaO of wood ash varies between 0.2 and 0.8, and depends on the habitat and geological substratum of the wood rather than on the tree species; ratios between 1.0 and 3.0 in wood‐ash glass are only possible when potash is added as a third base material. Melting temperatures of wood‐ash glass sensu stricto, termed K–Ca‐2, produced with the two raw materials quartz sand and wood ash, are between 1250°C and 1400°C, while those of three‐component‐glasses, termed K–Ca‐3, are between 900°C and 1250°C, according to the amount of added potash. Experimentally produced glass displays different hues, from colourless to brown, olive‐green and pink, according to the chemical composition of the wood ash. Elevated MnO concentrations between 0.5 and 3 wt% may originate from wood ash and are hence not necessarily an indicator of colour‐inhibiting additives. Phosphate stemming from wood ash is an essential discriminator between wood‐ash glass and potash–lime glass. Because wood ash contains only minor amounts of sodium, wood‐ash glass with equal concentrations of potassium and sodium is a hybrid glass type, where besides quartz sand, wood ash, possibly potash and also soda‐rich cullet have been applied for glass production.     

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.     

Characterization of some ancient glass beads unearthed from the Kizil reservoir and Wanquan cemeteries in Xinjiang,China

A total of 33 ancient glass beads unearthed from the Kizil reservoir cemetery and Wanquan cemetery in Xinjiang are studied using Raman spectroscopy, scanning electron microscopy with energy‐dispersive spectrometry (SEM–EDS) and other methods. The detailed study of the glassy matrices, the crystalline inclusions and the microstructural heterogeneities for these glass beads has revealed some valuable information to help in the understanding of their possible manufacturing technology and provenance. At least two different types of glass were present in the two cemeteries. For the first time, antimony‐based colourant/opacifier—for example, Pb₂Sb₂O₇ or CaSb₂O₆—was systematically identified in some beads of plant‐ash type soda–lime glass dated to about 1000–500 bc . The limited number of potash glass beads from the Kizil reservoir cemetery, which were dated to about 500–300 bc , used tin oxide as an opacifier. The diverse resources of the soda–lime and potash glasses indicate the existence of a complex trade network between China and the West much earlier than the Western Han Dynasty.     

Electron Microprobe Analysis of 9th–12th Century Islamic Glass from Córdoba,Spain

Twenty‐six samples from domestic assemblages of 9th–12th century Córdoba were subjected to electron microprobe analysis. The results reveal two main compositional types. The first, encountered in 13 of the samples, seems to result from the combination of plant ashes with high‐impurity sand, and has some contemporary parallels from Syria and Egypt. The second type is a lead–soda–silica glass, encountered in a relatively high proportion of the glasses (11 of the 26 sampled), possibly formed by the addition of lead metal to existing glasses and with very few known parallels. These are among a very small number of results available to date on the chemical composition of glasses from medieval Spain, and the presence of a high proportion of lead–soda–silica glasses is particularly interesting, possibly indicating a technological practice unique to, or originating in, the western Muslim world.     

AN ASSESSMENT OF COMPOSITIONAL AND MORPHOLOGICAL CHANGES IN MODEL ARCHAEOLOGICAL GLASSES IN AN ACID BURIAL MATRIX

The degradation mechanisms of glass in a buried context result in surfaces that have been depleted in various elements. The stability of the glass is primarily affected by the burial environment and the glass composition. However, in all archaeological glasses, the corroded layer that is formed on the surface tends to be low in alkalis, high in silica and lacking in cohesion. The extent to which the material has degraded, along with the physical nature of the corrosion, has a profound effect upon a wide range of factors affecting the stability of artefacts, as well as the choice of conservation techniques to be employed. This study has a number of objectives: determination of the morphology of the surface of the leached layer in glasses of two different compositions with different surface finishes; examination of the transition between the corroded material and the unaffected substrate; and investigation of concentration profile of different elements within the surface layers, as a function of depth. The study uses two glasses, fabricated under laboratory conditions, to replicate two common glass types found in the historical environment; a soda–lime–silica glass typical of those found in the Roman period throughout the Mediterranean and northwestern Europe, and high‐lime–potash glasses typical of those of Western Europe in the late medieval period. Three different surfaces have been prepared to mimic alternative manufacturing techniques such as blown, cast and ground surfaces for each composition. The glasses have been corroded under controlled laboratory conditions to replicate the buried environment. Imaging and chemical information is obtained using SEM–EDX and morphological information using IFM to produce 3‐D mapping from topographical surfaces.     

A COMBINED MULTI‐ANALYTICAL APPROACH FOR THE STUDY OF ROMAN GLASS FROM SOUTH‐WEST IBERIA: SYNCHROTRON μ‐XRF,EXTERNAL‐PIXE/PIGE AND BSEM–EDS

An integrated, multi‐analytical approach combining the high sensitivity of SR‐μXRF, the light element capability of PIXE/PIGE under a helium flux and the spatial resolution of BSEM + EDS was used to characterize chemical composition and corrosion of glass samples (first to fourth centuries ad ) from an important, but scarcely investigated, Roman region of south‐west Iberia (southern Portugal). The geochemical trends and associations of major, minor and trace elements were investigated to shed light on production techniques, the provenance of raw materials and decay mechanisms. The results, while confirming a production technique common to Roman glasses throughout the Empire—that is, a silica‐soda‐lime low‐Mg, low‐K composition, with glass additives as colouring and/or decolouring agents (Fe, Cu, Mn, Sb)—show at one site high Zr–Ti contents, suggesting a more precise dating for these glasses to the second half of the fourth century. The Ti–Fe–Zr–Nb geochemical correlations in the pristine glass indicate the presence of minerals such as ilmenite, zircon, Ti‐rich Fe oxides and columbite in the sands used as raw materials for the glass former: these minerals are typical of granitic‐type source rocks. The unusually high K content in the corrosion layers is consistent with burial conditions in K‐rich soils derived from the alteration of 2:1 clays in K‐bearing rock sequences.     

CHARACTERIZATION OF 18TH‐CENTURY MEISSEN PORCELAIN USING SEM–EDS*

Analytical investigations of fragmented Meissen porcelains well dated to between 1725 and 1763 have been carried out using SEM–EDS. The aim of the analysis was to characterize elements in bodies, glazes and overglaze enamels in order to create a baseline data set of materials used in the manufacture of porcelain at the Meissen factory, Saxony, during the 18th century. Analyses indicate body and glaze compositions to be consistent with a post c.1720–30 date, when a change from a lime‐rich flux to a potassium‐rich flux is documented to have occurred. Overglaze enamel compositions are shown to be consistent with contemporary accounts of enamel preparations at Meissen. Overglaze enamel compositions show that mixtures of pigments, in addition to documented enamel 18th‐century preparations, were in use at Meissen between c. 1725 and 1763.     

Radical changes in Islamic glass technology: evidence for conservatism and experimentation with new glass recipes from early and middle Islamic Raqqa,Syria*

The chemical analysis of excavated glass fragments from dated archaeological contexts in Raqqa, Syria, has provided a detailed picture of the chemical compositions of artefacts deriving from eighth to ninth and 11th century glassmaking and glassworking activities. Evidence for primary glass production has been found at three excavated sites, of eighth to ninth, 11th and 12th century dates; the first two are discussed here. The 2 km long industrial complex at al‐Raqqa was associated with an urban landscape consisting of two Islamic cities (al‐Raqqa and al‐Rafika) and a series of palace complexes. The glass fused and worked there was presumably for local as well as for regional consumption. Al‐Raqqa currently appears to have produced the earliest well‐dated production on record in the Middle East of an Islamic high‐magnesia glass based on an alkaline plant ash flux and quartz. An eighth to ninth century late ‘Roman’/Byzantine soda–lime recipe of natron and sand begins to be replaced in the eighth to ninth century by a plant ash – quartz Islamic soda–lime composition. By the 11th century, this process was nearly complete. The early Islamic natron glass compositional group from al‐Raqqa shows very little spread in values, indicating a repeatedly well‐controlled process with the use of chemically homogeneous raw materials. A compositionally more diffuse range of eighth to ninth century plant ash glass compositions have been identified. One is not only distinct from established groups of plant ash and natron glasses, but is believed to be the result of experimentation with new raw material combinations. Compositional analysis of primary production waste including furnace glass (raw glass adhering to furnace brick) shows that contemporary glasses of three distinct plant ash types based on various combinations of plant ash, quartz and sand were being made in al‐Raqqa during the late eighth to ninth centuries. This is a uniquely wide compositional range from an ancient glass production site, offering new insights into the complexity of Islamic glass technology at a time of change and innovation.     

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.     

Hydrogeochemical dynamics affecting steam‐heated pools at El Chichón Crater (Chiapas – Mexico)

El Chichón is an active volcano located in the north‐western Chiapas, southern Mexico. The crater hosts a lake, a spring, named Soap Pool, emerging from the underlying volcanic aquifer and several mud pools/hot springs on the internal flanks of the crater which strongly interact with the current fumarolic system (steam‐heated pools). Some of these pools, the crater lake and a cold spring emerging from the 1982 pumice deposits, have been sampled and analysed. Water–volcanic gas interactions determine the heating (43–99°C) and acidification (pH 2–4) of the springs, mainly by H₂S oxidation. Significantly, in the study area, a significant NH₃ partial pressure has been also detected. Such a geochemically aggressive environment enhances alteration of the rock in situ and strongly increases the mineralization of the waters (and therefore their electrical conductivity). Two different mineralization systems were detected for the crater waters: the soap pool‐lake (Na⁺/Cl^? = 0.4, Na/Mg>10) and the crater mud pools (Na⁺/Cl^? > 10, Na/Mg < 4). A deep boiling, Na⁺‐K⁺‐Cl^?‐rich water reservoir generally influences the Soap Pool‐lake, while the mud pool is mainly dominated by water‐gas–rock interactions. In the latter case, conductivity of sampled water is directly proportional to the presence of reactive gases in solution. Therefore, chemical evolution proceeds through neutralization due to both rock alteration and bacterial oxidation of ammonium to nitrate. The chemical compositions show that El Chichón aqueous fluids, within the crater, interact with gases fed by a geothermal reservoir, without clear additions of deep magmatic fluids. This new geochemical dataset, together with previously published data, can be used as a base line with which to follow‐up the activity of this deadly volcano.     

The Glaze Technology of Hispano‐Moresque Ceramic Tiles: A Comparison Between Portuguese and Spanish Collections

For the first time, Hispano‐Moresque glazed tiles from Portuguese and Spanish collections were studied together and compared. This work is included in a wider study tackling the technology of Hispano‐Moresque tile production from several collections in the Iberian Peninsula. While showing many similarities, differences were identified between collections, regarding both chemical and morphological characteristics. The collection from the Mosteiro de Santa Clara‐a‐Velha (Coimbra) stands out from the other collections, with higher SnO₂ content (up to 14 wt%), the highest Fe₂O₃ contents in amber glazes and a Ca‐rich interface layer (mostly comprised of wollastonite, CaSiO₃). Samples from Palácio Nacional de Sintra (near Lisbon) and Seville‐attributed samples (from the Instituto Valencia de Don Juan) are chemically similar, except that most Sintra's samples display a K‐rich glaze/ceramic interface, whereas the ones from Seville exhibit both K‐rich and Ca‐rich inclusions. The samples attributed to Toledo show glazes with many inclusions, contrasting with the homogeneous glazes in most Hispano‐Moresque tiles. From these results, we identify differences that can be used as markers in future studies on Hispano‐Moresque tiles.     

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.     

ANALYSIS OF LATE BRONZE AGE GLASS AXES FROM NIPPUR—A NEW COBALT COLOURANT

A multidisciplinary study of a unique group of Late Bronze Age (LBA) ceremonial glass axe heads and other artefacts shows that these are the first significant group of glasses coloured with cobalt to be identified from the Near East. The axes were excavated from the site of Nippur, in present‐day Iraq. Several are incised with the names of three kings, which dates the material to the 14th–13th centuries bc . Analysis by laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) indicates that the glass had high magnesia (MgO) and potash (K₂O) associated with a plant‐ash flux and was coloured blue by copper or a combination of copper and cobalt. These glasses are similar, but not identical, in major element composition to blue‐coloured glasses manufactured in ancient Egypt and elsewhere in Mesopotamia in the same period. However, the Nippur cobalt‐ and copper‐coloured glasses exhibit significantly different trace elemental compositions compared to Egyptian glass coloured with cobalt, showing that the ancient Near Eastern glassmakers had clearly identified and utilized a distinctive cobalt ore source for the colouring of this glass. Since it was previously thought that the only cobalt ores exploited in the LBA were exclusively of Egyptian origin, this new finding provides new insights on the origins of glass and how it was traded during the Bronze Age period.     

PRODUCTION TECHNOLOGY OF ROMAN LEAD‐GLAZED POTTERY AND ITS CONTINUANCE INTO LATE ANTIQUITY

A broad selection of Roman lead‐glazed pottery dating from the first century ad through the fifth century ad was studied to establish locations of workshops and to address their technology of production. The ceramic bodies were analysed by ICP–AES. In addition, lead isotope analysis was undertaken on a selection of glazes. These findings suggested that there were several regions responsible for the production of lead‐glazed ceramics in the western Roman world, including central Gaul, Italy and, probably, Serbia and Romania. Using the body compositions as a starting point, the glazing techniques employed by each of the potential workshops were examined using electron probe microanalysis. It was determined that there were two primary methods of glazing. The first method used lead oxide by itself applied to non‐calcareous clay bodies, and the second method used a lead oxide‐plus‐quartz mixture applied to calcareous clay bodies. Based on these data for clay composition and glazing method, transfer of technology from the Hellenistic east to the western Roman world was proposed. Likewise, the inheritance of lead‐glazing technology into late antiquity was established by making comparisons to lead‐glazed ceramics dating to the seventh to ninth centuries from Italy, the Byzantine world and Tang Dynasty China.     

A Quasi Non‐destructive Microsampling Technique for the Analysis of Intact Glass Objects By Sem/edxa

A novel sampling technique for the analysis of glass is described, which involves the removal of minute particles from an object with a diamond‐coated file, followed by energy‐dispersive X‐ray analysis in the scanning electron microscope (SEM/EDXA). The particles are fixed to adhesive carbon discs and carbon coated without grinding or polishing. Mean compositions are determined for 10 arbitrarily selected particles above a minimum grain size of 150 mm and normalized to totals of 100%. Tests were carried out on two standard soda–lime–silica glasses of well‐characterized composition, using two files of different grade. The analyses showed good agreement with the accepted values of all elements. Although the precision is somewhat reduced, this highly portable and quasi non‐destructive microsampling procedure provides almost the same information as that gained from samples embedded and polished in the normal way. Its application is thought to be especially useful for the investigation of intact glass objects and ceramic glazes.     

WASTE GLASS,VESSELS AND WINDOW‐PANES FROM THAMUSIDA (MOROCCO): GROUPING NATRON‐BASED BLUE–GREEN AND COLOURLESS ROMAN GLASSES

A collection of window‐panes, vessels and alleged waste from Thamusida has been investigated by OM, SEM–EDS, ICP–MS, ICP–OES and XAS at the Fe–K and Mn–K edges. Glass samples have been characterized as natron‐based soda–lime–silica glasses, with low magnesium and low potassium. The results have been compared with 43 reference groups available for ‘naturally coloured’ and colourless glasses of both Roman and later ages. Two main types were distinguished: RBGY 1 (R oman B lue–G reen and Y ellow 1) and RBGY 2 (R oman B lue–G reen and Y ellow 2). Given their compositional similarity to the Levantine I or, to a lesser extent, HIMT glasses, the Syrian–Palestinian coast for RBGY 2 and Egypt for the RBGY 1 have been suggested for their provenance. Most Thamusida samples have been assigned to the RBGY 2 type. A small group of Thamusida colourless vessels was included into the RC (R oman‐C olourless) compositional field; the latter still being defined. The alleged waste pieces may define a local production that should have been of secondary type. The investigations performed on local raw materials seem to discount the possibility of a primary glass‐making site. XAS measurements determined that Fe²⁺ contents ranging between 30 and 52% are able to assure an aqua blue colour; below 30%, the glasses turn light green or light yellow.     

Strontium Isotopes in the Investigation of Early Glass Production: Byzantine and Early Islamic Glass from the Near East*

⁸⁷Sr/⁸⁶Sr ratios have been determined for glasses from four production sites, dated to between the sixth and the 11th centuries, in the Eastern Mediterranean region. On the basis of elemental analyses, the glasses at each location are believed to have been melted from different raw materials. Two glass groups, from Bet Eli‘ezer and Bet She‘an, in Israel, are believed to have been based upon mixtures of Levantine coastal sands and natron, and have ⁸⁷Sr/⁸⁶Sr ratios close to 0.7090, plus high elemental strontium, confirming a high concentration of modern marine shell (⁸⁷Sr/⁸⁶Sr ~ 0.7092) in the raw materials. The isotopic compositions of these two groups of glasses differ slightly, however, probably reflecting a varying ratio of limestone to shell because the sands that were utilized were from different coastal locations. Natron‐based glasses from a workshop at Tel el Ashmunein, Middle Egypt, have ⁸⁷Sr/⁸⁶Sr values of 0.70794–0.70798, and low elemental strontium, consistent with the use of limestone or limestone‐rich sand in the batch. High‐magnesia glasses based on plant ash, from Banias, Israel, have ⁸⁷Sr/⁸⁶Sr values of 0.70772–0.70780, probably reflecting the isotopic composition of the soils that were parental to the plants that were ashed to make the glass. Strontium and its isotopes offer an approach to identifying both the raw materials and the origins of ancient glasses, and are a potentially powerful tool in their interpretation.