Ceramic technology. How to characterise ceramic glazes

Glazes add value to ceramic, improve its appearance (colour and shine) and make it waterproof. Through the choice of colours and designs, glazes made ceramics fashionable, even luxurious, and therefore, an object of trade. Each region and ruling dynasty developed its own style or trademark which makes them particularly suitable for dating purposes. Therefore, the study and analysis of glazes offers direct information about the acquisition of technical skills (technology), trade of specific materials (interregional links), migrations and the introduction/adoption of new trends. A ceramic glaze is a thin glassy layer fused to the surface of a ceramic body through firing. The interaction between the glaze and the ceramic body results in the interdiffusion of elements between both. A glaze consists mainly of an amorphous phase, but also includes bubbles, cracks and crystalline phases (undissolved compounds and crystals formed during the firing). Finally, the glazes were also decorated, and a large variety of materials and methods of applying the decorations were used. In this chapter, we present a summary of the technical characteristics of glazes (composition, microstructures and technical requirements), their discovery and use throughout history and decorative techniques. The methodology and analytical techniques to obtain the information are also discussed.Peer ReviewedPostprint (author's final draft

The ways of the lustre: looking for the tunisian connection

Recent excavations at the Fatimid and Zirid site of Sabra al-Mansuriya near Kairouan (Tunisia) provide the first evidence of lustreware production in medieval Ifriqiya, in the 10th–11th centuries AD. As the Fatimid dynasty moved from Ifriqiya to Egypt to establish its capital in Fustat (Cairo), technological connections with the Egyptian lustreware could be expected. Tunisian lustreware may also be the link in the transmission of the technique towards Muslim Spain. It represents a new piece of the puzzle of understanding the diffusion of lustre technology from the East to the West of the Mediterranean. The composition and microstructure of the bodies and glazes, and the micro- and nano-structure of the lustre layer are compared in a preliminary approach to the technological relationships between Tunisian, Egyptian, and Spanish lustrewares.Peer ReviewedPostprint (published version

Glaze production at an early Islamic workshop in al-Andalus

This is a pre-print of an article published in Archaeological and Anthropological Sciences. The final authenticated version is available online at: https://doi.org/10.1007/s12520-018-0666-y.The study and analysis of the materials found in one of the earliest Islamic glazed ceramics workshop in al-Andalus (Pechina) dating from the second half of the 9th century, including fritting vessels, kiln furniture, wasters and slags, and a glass chunk, have revealed the materials used and methods of production. Galena was oxidised to obtain PbO in the workshop. Fritting of the glaze involved a two-stage process for which two different types of vessels were used. The fritting process ended with a melt which was poured to obtain a high-lead glass. The ground glass was applied over the biscuit-fired ceramics, and fired to a temperature high enough to soften the glaze and adhere it onto the ceramic surface. Evidence of a similar process was found in a later workshop in San Nicolas (10th century) which demonstrates the persistence of the technique in al-Andalus during the caliphal period. There is little evidence of early Islamic glaze manufacture at kiln sites, and in contrast to the glass workshops, the glazed ceramics workshops have not been studied. Consequently, this study adds valuable information to the currently very limited knowledge about the early glaze technology in Dar al-Islam.Peer ReviewedPostprint (author's final draft

Primeros resultados del estudio analítico de la cerámica vidriada decorada Nazarí: la cerámica palatina (ss. XIV-XV)

lustreware, decorations, glazes, analyses, céramique a réflex métallique, décorations, glaçures, analyses, cerámica dorada, decoraciones, vidriados, análisisPostprint (published version

The colour and golden shine of early silver Islamic lustre

A selection of lustres including 9th century AD polychrome and 10th century AD monochrome Abbasid lustres from Iraq, and 10th to 12th centuries AD Fatimid lustres from Egypt and Syria is studied in the present paper. The selection is based on previous studies that demonstrated that all of them contain metal silver nanoparticles and copper, which, when present, appears either as Cuþ or Cu2þ dissolved in the glaze. They show different colours, green, yellow, amber, and brown, and may also show or lack a golden-like reflectivity, which results mainly from average size and concentration in the layer of the silver nanoparticles. In this paper, a depth profile composition of the lustre layers is determined using Rutheford Backscattering Spectroscopy, allowing the determination of the total silver content, concentration of silver, copper to silver ratio, and thickness of the lustre layers. We show that the enhanced golden-like reflectivity occurs only for layers with a high concentration of silver, and that the addition of PbO to the alkaline glaze helps the formation of more concentrated layers. The results obtained provide new hints concerning the lead enrichment of the glazes during this period.Peer ReviewedPostprint (published version

Análisis arqueométrico de la cerámica dorada andalusí de la Alcazaba de Onda (Castellón)

In the present article there are exposed the results of the analysis of the bodies and the glazes of 21 ceramic representative fragments of a set found in the excavations of the Alcazaba of Onda and that can be dated in outline between ends the XIth and the first half of the XIIth centur y. We have attended fundamentally to the lustre potter y and to the ceramics with white cover. The principal aim is to determine if it is a question of one or of several productions. For it there has been analyzed the composition and texture of the body, as well as the microstructure and composition of the glaze by means of microscope electronics of sweep (SEM). Also there have been compared with ceramics that we suppose local, such productions as common ceramics of the same archaeological context and fragments found in the califal arqueological site Mas de Pere, where kilns were situated for the manufacture of ceramics. Also we have arranged with clays of the nearby deposit of the Sitjar. The results show that there are different productions of lostre ceramics, both for composition of the bodies and for the glaze. In addition, the composition of the white ceramics is ver y similar to the local clays of Onda, with which it is not possible to reject that it was a question of a local production.Postprint (published version

Estudi arqueomètric dels forns i producció ceràmica d'un taller romà de Llafranc

The walls of some kilns of a roman workshop and their ceramic production have been studied by XRD and XRF. From the chemical composition and by means of a multivariant analysis the samples are grouped by chemical affinity. By the other side, and from the XRD analysis the firing conditions of the ceramic productions have been established. These results are in agreement with those obtained on the walls of the kilns

Technology of production of Syrian lustre (11th to 13th century)

Lustre is a decoration consisting of a surface layer of silver and copper metal nanoparticles, a few hundreds of nanometres thick and incorporated into the glaze. It shows a colourful metallic and iridescent appearance which makes use of the quantum confined optical response of the metallic nanoparticles. Three apparently unrelated lustre decorations, yellow-orange golden (Tell Minis), a dark brown-reddish with iridescences (Raqqa) and yellow-brown golden (Damascus) were produced in the same area in successive periods over tin and lead-free glazes which is known to require specific strategies to obtain a metallic shiny lustre. The composition and nanostructure of the lustre layers are analysed and the materials and specific firing conditions followed in their production determined. The optical properties of the lustre layers have been analysed in terms of the nanostructure obtained and correlated to the specific processing conditions.Peer ReviewedPostprint (author's final draft

Lustre and glazed ceramic collection from Mas Llorens, 16-17th centuries (Salt, Girona). Provenance and technology

Lustre pottery unearthed at Mas Llorens constitutes one of most interesting collections of late 16th and early 17th centuries lustre pottery from Catalonia. The collection is formed by an unparalleled set of more than 200 complete dishes and bowls, which were buried in the same place and at the same time, thus becoming of paramount archaeological interest. Consequently, this set of lustre pottery has become of pivotal importance for the study of this type of ceramic not only because of the number and integrity of the pieces that were found, but also by its homogeneity. This multidisciplinary study has revealed the importance of this pottery in terms of economy, trade, and social status in Modern times Catalonia. The main purpose of this paper is to determine provenance and technology of production of lustre and other glazed wares from Mas Llorens. We present the results of the archaeometrical characterization of 21 ceramic sherds, recovered from the excavations of Mas Llorens. The sampling includes 11 lustre ceramics, 4 blue-on-white tin-lead-glazed ceramics, and 6 plain lead glazed objects. Chemical and mineralogical composition of the ceramic pastes were analyzed by XRF, NAA, and XRD, and statically compared to 16th-17th tin-lead glazed pottery produced by the main Catalan workshops (e.g. Barcelona, Reus, Vilafranca del Penedes). The chemical data show a high homogeneity in the composition of lustreware pastes, as seen in other proto-industrial fine ceramic productions, evidencing a Barcelonan provenance. Chemical composition and microstructures of the glazes and lustre decorations were observed and analyzed by Scanning Electron Microscopy (SEM), Electron Probe Microanalyzer (EPMA) and Elastic ion backscattering spectroscopy (EIBS). Successful lustre exhibits a red-copper color and metallic shine; it contains more copper than silver (average concentration, 9.5 wt% and 3.4 wt% respectively) with a ratio of wt% Cu/(Cu+Ag) = 62%, in the form of copper and silver nanoparticles which are concentrated in a thin layer (<300 nm) very close to the surface. On the contrary, in the unsuccessful brown lustre lacking metallic shine, although the copper to silver ratio is similar - wt% Cu/(Cu+Ag) = 63% -, the copper nanoparticles are distributed in a thick layer (1 micron thickness) but in lower concentration (average concentration in the layer 3.4 wt%), while the silver nanoparticles appear concentrated on a thinner surface layer. The lack of metallic shine in those samples is explained by the low concentration of silver and copper nanoparticles in the layer. This may be related to a deficient reducing firing capable of reducing copper to the metallic state and stopping its diffusion into the glaze.JMM and TPC are indebted to the project MAT2013-41127-R funded by Ministerio de Ciencia e Innovación (Spain). TP is indebted to the project 2014 SGR 00581. JGI is indebted to IKERBASQUE Basque Foundation for Science. The laboratory work at MURR was supported in part by National Science Foundation grants (0102325, 0504015, 0802757)Peer ReviewedPostprint (published version

Manganese brown decorations in 10th to 18th century Spanish tin glazed ceramics

In this study we will show the differences in the technology of production of the manganese decorated glazes from early black and green Caliphal pottery (10–11th century AD) from Murcia; green and brown Hispano–Moresque productions (13–14th century AD) from Valencia and Catalonia; and manganese brown decorations (17th century AD) from Barcelona. SEM–EDX and μ-X-ray diffraction performed at the European Synchrotron Radiation Facility (ESRF) have been carried out on polished thin cross sections (about 50 μm thick) of the decorated glazes. Braunite, kentrolite, bustamite and hausmannite have been identified in the brown decorations. Differences and similarities in the nature and microstructure are presented and related to differences in the production process