DISCOVERY, PRODUCTION AND USE OF TIN-BASED OPACIFIERS IN GLASSES, ENAMELS AND GLAZES FROM THE LATE IRON AGE ONWARDS: A REASSESSMENT (original) (raw)
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Tin-based opacifiers in archaeological glass and ceramic glazes: a review and new perspectives
Journal of Archaeological and Anthropological Sciences, 2018
Tin-based opacification by tin oxide and lead-tin-oxide particles was used in glass production since the first millennium BC and in ceramic glazes since the eighth century AD. Opacification process is often characterised by significant amounts of tin oxide and lead oxide dispersed into glassy matrices or by identification of the opacifying particles by means of microstructural or (micro-)XRD analyses. The processes of opacification and manufacture are usually more difficult to establish from compositional and microstructural analyses because they leave little diagnostic traces. This review aims to integrate compositional data on archaeological glass and glazes and in particular the Pb/Sn values, with descriptions of the opacification processes in historical treatises, observations at traditional workshops, and the results of previous replication experiments to shed further light on technological issues underlying these methods of opacification and highlight new research perspectives.
The Beginnings of Tin-opacification of Pottery Glazes (1997)
Ltrhorrrtor:\fhr Archrrrology mid the Himi:\. of Art. O.\,fortl Uriiwrsitx, 6 Keble Rotrd. O.rfbrrl, OXI 3QJ. UK I .? ' Wesi Asicrn Deprrriiireirt. Ro,vtrl Oirrtrrio Musrirrrr. 100 Quccir 's fw!i, 7ororrto. Onttrrio. MSS 2C6. Ctintrdti A rtt~~ltidi.sc~iplinrit~ pr~igriitrrrne of resetiruh on the gltr:eel c~ercirnics r,f the Islamic world IINS been ,focused on clue.stiorr.s of their duting, pro~wniiric~c~ rind technology. One pcirticulitr ilite.stion hiis been tire devrloi~~tnent of tin-opic~fird glii:e.s. r i n d tkr niititre of glci:e opiic$ccition gerzercilly in the lsl~itnic ~corld. Tl~e,firtding.s of'rlie ~wrious studies coiitbine to indicate tlzcit tin w i s , f i t -s t u.sd c.r~~c~rinrrntcilly in Bci.srLr, Iriril, in the first hiilf'i?f'the eighth centup AD, tippcirently within the context of pre-lslnmic opnyiie-gl~i:e technology. Over the course of the next century. ( i n opciyiie-glaze technology entirely reliimt on tin oxide inclusion.^ w(is developed in I r q rind Egypt (itid, subsrquentlv. this technology spreud to the rest of the Isliintic world rind d s o to Europe.
Journal of Archaeological Science (97), 2018
It has been generally accepted that the beginnings of tin-based opacification of ceramic glazes is associated with the white glazed wares excavated in Iraq and western Iran and dated to the ninth century AD (so-called 'Samarra-type' pottery). This paper focuses on an earlier stage in the technological development of tin-opacified glazes, that is, the yellow and white glazed wares produced from the eighth century AD in Egypt and the Levant. In addition, the compositional data was extended for the subsequent spread of tin-opacified glazes into Mesopotamia in the ninth century and Northern Iran and Central Asia in the tenth century. Using SEM-EDS and SR-Micro-XRD, the chemical composition and microstructure of eighty-five samples of opaque yellow and white glazed wares from Egypt (Fustat), the Levant (Madaba, Aqaba, Al-Mina and Raqqa), Mesopotamia (Samarra, Kish, Basra and Susa), Northern Iran (Takht-i Suleiman), and Central Asia (Nishapur, Merv and Samarqand) were investigated. These data confirmed that the yellow and white glazes were opacified by lead-tin-oxide (PbSnO 3) and tin oxide (SnO 2) particles respectively. Replication experiments were then conducted to imitate typical compositions of the analysed opaque yellow and opaque white glazes. Overall, the results posited the beginning of tin-based opacification of glazes in the eighth century in Egypt and the Levant, and provided explanations as to how the production of opaque yellow and white glazes in the Levant and Mesopotamia might have been technologically linked.
Revisiting the beginnings of tin-opacified Islamic glazes
The generally accepted theory is that the demand for Islamic glazed pottery started in Abbasid Iraq in the 9th century AD with the production of a range of glazed wares in response to the import of Chinese stonewares and porcelains. However, Oliver Watson has recently proposed that the demand for Islamic glazed pottery first occurred in Egypt and Syria in the 8th century AD resulting in the production of opaque yellow decorated wares. Using a combination of SEM analysis of polished cross-sections, and surface analysis using hand-held XRF or PIXE, Coptic Glazed Ware from Egypt, Yellow Glazed Ware from Syria, and comparable wares from Samarra, Kish and Susa have been analysed. The analyses show that the opaque yellow decoration was the result of lead stannate particles in a high lead glaze, which it is suggested was produced using a lead-silica-tin mixture. The use of lead stannate in the production of yellow opaque glazes is explained in terms of technological transfer from contemporary Islamic glass- makers who continued the Byzantine tradition of glassmaking. It is further argued that the introduction of opaque yellow glazed pottery into Mesopotamia could have provided the social context for the sudden emergence of tin-opacified white glazed pottery in Abbasid Iraq in the 9th century AD. However, in view of the very different glaze compositions employed for the yellow and white opaque glazes, it seems probable that the white tin-opacified glazes used for Abbasid cobalt blue and lustre decorated wares represent a separate but parallel technological tradition with its origins in the production of Islamic opaque white glass.
Journal of Archaeological Science, 2018
The earliest glazed ware in al-Andalus is dated to the Emiral period (c. AD 850-875) and is not until the Caliphate of Córdoba (AD 929-1031) that a distinctive polychrome tin glaze started being produced. A short transition period (c. AD 875-925) in which elaborate monochrome and bichrome transparent glazes wares coexist with polychrome transparent and tin opaque glazed wares has been identified. The existence of a polychrome lead transparent glaze production in al-Andalus wares is demonstrated; it has distinctive composition and methods of production from monochrome and bichrome wares, and shares a distinctive absence of foot and overglaze application of the decorations with the tin-opacified wares. With regard to the possible routes of the introduction of the polychrome lead and tin glazes into the western Mediterranean the Tunisian connection seems completely discarded. Moreover, and although some similarities between the Cordoba and the Abbasid productions such as similar tin glaze recipe and decorative patterns and use of lead glazes, can be traced, the dissimilarities, such as, the use of overglaze decorations, absence of alkali transparent glazes, variances in the tableware shapes and absence of foot, are still more important, and do not support a clear link between them.
Analytical and Bioanalytical Chemistry, 2002
Samples from Greek figure vases were investigated by scanning electron microscopy coupled with energy dispersive X-ray analysis, X-ray diffraction, thermomechanical analysis and reflectance spectroscopy to achieve a technological characterisation. The vases, dating from the end of the sixth to the fourth century BC, had been excavated at Locri Epizephiri (Calabria, Italy) and attributed to Attic or local workshops, respectively. Information on the morphology of black slip areas and firing temperatures was compared with that previously obtained for Attic and local black gloss pottery from the same site; results show that the peculiar technique required for the production of black slips was mastered by both Attic and local potters and employed for monochrome and figured products. The black coating is usually well vitrified and 15-to 20-lm thick; the evaluated maximum firing temperature is around 900°C, while a temperature lower than 800°C is generally estimated for ceramic body re-oxidation.
Chemical and Textural Characterization of Tin Glazes in Islamic Ceramics from Eastern Spain
Journal of Archaeological Science, 2001
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 Có rdoba 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 SnO 2 (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.
LEAD GLAZES IN ANTIQUITY?METHODS OF PRODUCTION AND REASONS FOR USE
Archaeometry, 1998
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.
OPTICAL PROPERTIES OF TIN-OPACIFIED GLAZES
Archaeometry, 2000
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.
Journal of Archaeological Science: Reports, 2020
Late 15th century tin glazed stove tile fragments from Bern, Fraubrunnen and Nidau are among the oldest witnesses of this advanced glaze technique in Switzerland and coexist with traditional lead glazed tiles. On a single tile, both glazes can also occur (two-glaze technique). In this SEM-BSE and -EDS study, bodies, slips and glazes of 14 tin and 2 lead glazed tiles were examined in order to constrain the raw material sources, the recipes, the application technique and the firing parameters. Mostly all ceramic bodies are of the traditional low Ca type. With the exception of two samples, they all have a slip that either belongs to the traditional quartz-rich, CaO-poor and SiO2-rich type I or a new CaO-rich type II. The latter is the earliest known use (so far) in tin-glazed stoves from Switzerland. Slip I can be found under both glazes, slip II only under tin glazes. Uncovered or slip covered bodies were biscuit fired before glazing. Firing temperatures were mostly in the range 950-1050oC. Important chemical exchanges between the liquid glazes took place during firing. The lead glazes digested minerals of the latter, while lead infiltrated the porous ceramic substrate. The transparent monochromatic lead glazes are green with Cu, or yellow and brown, depending on the Fe content and the presence or absence of a slip. The opaque tin glazes have SnO2 concentrations of 6-17 mass%. Objects with two-glaze technique show 4 of the 6 possible combinations of slip and glaze types. This indicates that the potters did not follow a unique (new) recipe, but tried many mix of old and new techniques.