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In recent decades, the production techniques of azulejos (Portuguese glazed tiles with a predominantly blue colour) remain a subject of ongoing research. Combining historical research with advanced analytical techniques, this communication aims to show the pigments and materials that define the azulejo colour palette, along with their production recipes and the chemical and structural composition of the glazed tiles. This communication highlights the application of synchrotron radiation to the analysis of Portuguese azulejos. Some examples will be presented, namely the Co and Cu K-edge X-ray absorption near-edge spectroscopy (XANES) results performed on glazed tiles from the Fronteira Palace, in Lisbon and the speciation of pigments from Pena National Palace, Sintra. The speciation state of certain chemical elements provides an understanding of their role as chromophores, glass network formers or modifiers, contributing to a deeper knowledge of the production techniques, provenance, and the tiles’ history of use. The non-destructiveness nature, allied to the high-resolution capabilities of synchrotron radiation chemical imaging, offer a unique tool for investigating cultural heritage materials, enhancing our understanding of their composition, structure, and degradation processes, and contributing to their long-term preservation and interpretation for future conservation efforts.

The Portuguese azulejo (glazed tile) heritage is internationally recognised as unique, much due to its original and uninterrupted use in the most diverse architectural spaces since the 16th century. This heritage has been given increasing attention in the last decades; however, its production techniques are still being studied.

In 2021, the ChromAz project, funded by the Fundação para a Ciência e a Tecnologia (PTDC/HAR-HIS/1899/2020), began a 3-year study on the colours used in Portuguese azulejo since its beginning in the late 16th century until the mid-18th century.

The project was designed to investigate three main axes of azulejo heritage: colour palette, recipes, and chemical composition. This communication addresses the methodology and work completed so far.

The methodology combines historical research with the analytical characterisation of selected samples to identify the pigments that make up the Portuguese tile palette. The collection of the National Tile Museum in Lisbon was the starting point for wider research on the colours used during the period under study. Important in situ panels (e.g., the Academy of Sciences and the Calheta Palace, in Lisbon) are being studied as well. A multi-analytical methodology covering elemental, molecular and structural analysis was developed to enable the identification of all glaze components.

Contrary to Italian maiolica or Dutch delftware, there are no known treatises or recipe books on Portuguese ceramics before the 19th century, making the historical tiles the sole testimonies of practical knowledge that has been lost over time. Therefore, the results obtained from the chemical analysis are the basis for the reproduction of the colours, along with the study of historical treatises and recipe books, such as the Italian treatise on maiolica by Cipriano Piccolpasso (“The Three Books of the Potter’s Art”, ca. 1557).

This project is a collaboration between several institutions: VICARTE (Glass and Ceramic for the Arts – FCT-NOVA), Universitat Politècnica de Catalunya (BarcelonaTech – Spain), Laboratory for Instrumentation, Biomedical Engineering and Radiation Physics (LIBPhys, FCT-NOVA - Portugal), the University of Antwerp (Belgium), the ARTIS - Institute of Art History (FLUL - Portugal), and the National Tile Museum (Lisbon, Portugal).

Decorated wall tiles known as azulejos form one of the most important pieces of Portuguese cultural heritage, as well as the country’s most original contribution to Europe’s artistic heritage. Thanks to multiple influences from Spain, Italy and the Flanders, a local tradition emerges towards the end of the 16th century and quickly becomes widespread.[i] Combining long-lived technological traits with innovation, the chromatic palette of Portuguese tiles went through a period of expansion in these initial decades. Besides white and blue, panels show brown and purple decorations, as well as various shades of yellow, orange and green. But while elsewhere in Europe we have treatises detailing how glazed ceramics were painted and what pigments were employed, the complete lack of such sources in Portugal severely hinders our understanding of artistic practices connected with azulejos.

Thanks to the efforts of heritage and conservation scientists who addressed the issue by turning to the analysis of the tiles themselves, a picture has started to emerge around the technology of tile manufacture. [ii][iii][iv] In line with current European practices, a number of metallic oxides were used to achieve the various colours. Among these substances, lead antimonate (Pb2Sb2O7) appears to occupy an especially relevant spot. Mixed with various reagents, lead antimonate was found in yellow, orange, brown and olive-green pigments. But what recipes did painters adopt to make their colours? And do these recipes change significantly over time?

Using a technical historical approach which combines the chemical analysis of historical tiles with the laboratory replication of pigment recipes, this poster addresses the role of lead antimonate within the colour technology of Portuguese azulejos. First, a number of pigments were reworked following historical majolica recipes. These include lead antimonates modified with zinc, tin or iron oxide, as well as a mixture of lead antimonate yellow and cobalt blue. The pigments were then painted on test tiles over a powdered white glaze and fired again. The presence and quantity of the different ingredients were found to strongly influence the colour, resulting in a broad spectrum of pigments spanning from pale yellow to dark orange and olive green. This shows how small adjustments to the lead-antimony base provided artists with an extensive palette, thus accommodating their chromatic needs.

In order to check our replicas against historical azulejos, an assemblage of 16th to 18th-century tiles from the Museu Nacional do Azulejo in Lisbon was analysed by scanning electron microscopy (SEM-EDS). Our results indicate that several lead antimonate-based pigments and pigment combinations were used across time. Besides the lead-antimony base, we found evidence of yellow, orange and brown decorations achieved through the addition of zinc, tin and iron, or mixtures of them. As for olive greens, these were always achieved by combining one of the base yellows available with a cobalt blue pigment, a peculiarity restricted to Portugal.

Most importantly, we found that some of our replicas match the composition of historical azulejos, allowing us to identify what pigment recipes were used by Portuguese artists, therefore shedding some precious light on the technological and artistic practices at the core of one of Portugal’s most renown pieces of cultural heritage. 

[i] Pereira, S.R.M., G. Conte, L. Esteves, A. Pais, J. Mimoso – Evolution of azulejo glaze technology in Portugal from the 16th to the onset of the 19th century. Journal of the European Ceramic Society, 43, (2023), 3804-3815.

[ii] Coentro, S., J. Mimoso, A.M. Lima, A.S. Silva, A. Pais, V.S.F, Muralha – Multi-analytical identification of pigments and pigment mixtures used in 17th century Portuguese azulejos. Journal of the European Ceramics Society, 32, (2012), 37-48.

[iii] Guilherme, A., V.D Hodoroaba, S. Benemann, J. Coroado, M.L. Carvalho – Morphological and compositional features of blue and yellow pigments used in Portuguese glazed ceramics by SEM/EDX – unravelling manufacturing differences. J. Anal. At. Spectrom., 29, (2014), 51-57.

[iv] Bandiera, M., U. Veronesi, M. Manso, A. Ruivo, M. Vilarigues, L. Esteves, A. Pais, S. Coentro – The colour palette of 17th-18th century azulejos: a multi-analytical non-invasive study. Journal of Cultural Heritage (forthcoming)

The Lisbon Academy of Sciences occupies part of the former Convent of Nossa Senhora de Jesus of the Third Order of St. Francis. The 18th-century renovation of the cloister is well explained on the pillar W/S, mentioning the completion of the works, including the tilework, in 1715. There is some archive documentation as well. However, this does not make it easier to understand the different remaining azulejos and “who did what”. It is known that there was a first intervention in 1712-13, paid to the tiler António de Abreu, and in 1713, there was a payment to the painter António de Oliveira, certainly António de Oliveira Bernardes. In 1714, another tiler, António de Oliveira, was hired to continue the work, covering two and a half wings of the cloister, as one had already been completed. This document mentions that the previous campaign shows different mistakes that should now be avoided, both in terms of the quality of the tiles and the laying, explicitly stating that the tiles should be "of a good blue colour". The payment records also show that the tiles were supplied by the potter Francisco dos Santos. On top of that troubled process, since then, tiles have been extensively intervened – there are 18th-century restorations, replicas, and so forth.  

At this time, Portuguese azulejo was going through its “golden era” – the “blue-and-white” period or the Masters’ Cycle. Authorship issues have been addressed within the Art History field, although many azulejo panels remain without a secure author. The collaborative process within the workshops has also been considered to address the different roles involved in the production process. More recently, material characterisation studies have contributed to a better understanding of the materials and techniques used in Portuguese azulejo workshops. By combining these two approaches, we can further advance the knowledge of painters’ techniques and workshop practices and, hopefully, unveil current authorship and provenance questions.

This study intends to provide new data through a multidisciplinary approach that correlates historical and visual information with the material characterisation of the azulejos from the Lisbon Academy of Sciences. Other decoration campaigns until the 20th century were also considered and characterised. The methodology combined in situ analyses by portable X-ray Fluorescence (p-XRF) and colourimetry (CIE L*a*b*) with laboratory analyses of polished cross-section samples by µ-Raman spectroscopy and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS). For the latter, samples were collected only from tile fragments in storage. This methodology is part of a wider project focused on the identification and characterisation of the chromatic palette used in 16th- to 18th-century azulejos (ChromAz). Results will be discussed considering the different sets of panels, their colour shades, and the chemical and morphological characteristics of their azulejos.

Beginning towards the end of the 16th century, the chromatic palette of Portuguese decorated tiles (azulejos) expanded dramatically. Besides white and blue, the colours now include purple, brown and different shades of yellow, orange and green. Although the lack of local sources severely limits our knowledge of how the colours were achieved, existing analytical data suggest that lead antimonate (Pb2Sb2O7) is one of the most frequently recurring compounds in pigment mixtures. Known as Naples yellow, lead antimonate represents the main component of yellow pigments and, mixed with a number of other oxides, formed the base for olive green, orange and orange-brown.

Using a technical historical approach, this paper addresses the role of lead antimonate within the colour technology of Portuguese azulejos. First, an ensemble of historical azulejos (16th-18th century) was investigated through a multi-analytical approach, to obtain information on their chemical composition (EDXRF) and to identify the main colouring agents (UV-VIS FORS and µ-Raman spectroscopy). Moreover, colourimetric measurements of the different hues were performed to address the relationship between colour and chemical composition. All analyses were performed non-invasively on the surface of the tiles. Our results confirm the widespread use of lead antimonate, on its own (yellow) or in combination with zinc (orange), iron (brown) and cobalt (olive green).

Further to the work on historical samples, a number of lead antimonate-based pigments were replicated in the laboratory following contemporary recipes from the Italian majolica tradition. Once obtained, the pigments were applied on test tiles, over a white glaze, and fired again. The resulting tiles were analysed with the same suite of techniques. Micro Raman indicates that the molecular profile of test tiles matched that of the historical ones, confirming the role of lead antimonate as the main compound in many of the colours. Our replications also confirm that additional ingredients strongly affect the hue, as is the case of alkali fluxes, zinc or tin oxide. On the other hand, the addition of smalt, a cobalt-based preparation, or copper oxide, gave olive green decorations, while the presence of iron oxide turned the pigment a dark orange to brown.

This article sheds new light on the role of lead antimonate as the main ingredient in three major colours found in Portuguese tiles. Our experiments show that by skilfully dosing a variety of reagents in the pigment recipe, painters could count on a rich palette of hues to accommodate their chromatic needs.

The chromatic palette of Portuguese azulejos in the first half of the 17th century presented a diverse set of colours ranging from blue and white to different shades of green and yellow, through to orange, purple and brown. Despite the enormous importance of azulejos in the history of Portuguese art, we have no primary sources on how to prepare the colours and glaze the tiles.

The aim of the present paper is to shed light on the colouring technique of an assemblage of 17th to 18th-century Portuguese glazed tiles (azulejos), stored in the National Tile Museum (Lisbon, Portugal). The study includes the characterisation of each colour through a suite of analytical techniques. SEM-EDS and EDXRF were employed to obtain qualitative and (in some samples) quantitative information on their chemical composition. UV-VIS FORS and µ-Raman spectroscopy allowed us to identify the main colouring agents. Finally, to address the relationship between colour and chemical composition, colourimetric measurements were performed as well. To further understand the production of different shades of analysed colours, a number of pigments were replicated following historical recipes from Renaissance treatises.

The analytical results of historical tiles’ experimental replications show that Portuguese painters followed traditional pigment recipes. The colours were obtained through a few base ingredients, namely cobalt (blue), lead antimonate (yellow/orange), manganese (purple), iron (brown) and copper (green). Moreover, by combining some of these components and by adding specific reagents, the palette could be widened to a variety of shades.

This multidisciplinary approach offers key insights into artistic practices and technological choices, filling the gap left by the absence of textual evidence. Our results reaffirm the importance of technical art history as a cross-disciplinary approach to the study and preservation of cultural heritage.

This work  aims to study the colours used to paint 22 Portuguese glazed tiles (azulejos) stored in the National Tile Museum, in Lisbon, Portugal. The tiles are dated from the 17th to 18th century and represent different colour combinations used throughout several decades.

Building on a previous study where the basic chemical composition of the 17th-century colour palette was identified [1], we used a non-invasive methodology to further identify compositional differences among identical colours within a wider timeframe.

The colours (blue, white, yellow, orange, purple, green and brown) were analysed by EDXRF to obtain qualitative and (in some samples) quantitative information on their chemical composition. UV-VIS FORS and µ-Raman spectroscopy were used to identify the main colouring agents. Finally, colourimetric measurements of the different hues of each colour were performed to address the relation between colour and chemical composition. All analyses were performed on the surface of the tiles.

The analytical results showed that green colour could be obtained through copper base pigment or a mixture of a lead-antimonate-based pigment and a cobalt-blue pigment. Although cobalt is the colouring agent of the blue pigments, the compositional differences detected through the analyses suggest using different raw materials or adding other elements to modify the hue.  On the other hand, different yellow hues (from lemon-yellow to orange) were manufactured by mixing lead-antimonate base pigment with zinc, tin, or iron oxide. A manganese ore was used to make the purple pigment.

[1] Coentro, S., Mimoso, J., Lima, A., Silva, A., Pais, A., & Muralha, V. (2012). Multi-analytical identification of pigments and pigment mixtures used in 17th century Portuguese azulejos. Journal of the European Ceramic Society 32, 37-48

The chromatic palette of Portuguese azulejos (decorated tiles) went through a period of expansion from the 16th to the 17th century. Besides white and blue, panels show brown and purple decorations, as well as various shades of yellow, orange and green. Since no local sources are available, we have limited information on how the many colours were achieved. What we know from the data gathered so far is that among the materials employed to make the pigments, lead antimonate (Pb2Sb2O7) appears to occupy an especially relevant spot. Also known as Naples yellow, lead antimonate was the main component of yellow decorations. Mixed with other ingredients, lead antimonate yellow formed the base for two other key colours, namely olive green and orange-brown.

This paper addresses the role of lead antimonate as the base to make pigments used to decorate Portuguese azulejos. Following historical majolica recipes, a number of preparations were replicated in the laboratory. The pigments synthesised were then painted on test tiles, over a white glaze, and fired again. It was observed that where lead antimonate was the main ingredient, the result is a yellow decoration. The presence and quantity of reagents such as alkali fluxes, zinc or tin oxide were found to strongly influence the colour, resulting in a broad spectrum of hues. On the other hand, the addition of smalt, a cobalt-based preparation, or copper oxide, resulted in olive green decorations, while the presence of iron oxide turned the pigment a dark orange to brown.

The molecular and chromatic profile of all the pigments produced were also characterised. Micro Raman analyses confirmed that Naples yellow is the main crystalline phase in all colours, with characteristic bands that indicate the presence of different reagents according to the colour. Colorimetric coordinates further confirm that by mixing different ingredients into the lead antimonate base, pigments go from pale yellow to brown to olive green.

This article sheds new light on the use of lead antimonate as the main ingredient in three major colours found in Portuguese tiles. Our experiments show that by skilfully dosing a variety of reagents in the pigment recipe, painters could count on a rich palette of hues to accommodate their chromatic needs.

The chromatic palette of Portuguese azulejos expanded dramatically during the 17th century, with colours ranging from blue and white to different shades of green and yellow, through to orange, purple and brown. Despite the enormous importance of azulejos in the history of Portuguese art, we have no primary sources on how to prepare the colours and glaze the tiles.

This paper presents data from an ongoing research project that investigates the chromatic history of Portuguese azulejos through their colour chemistry. We started with yellow, a very versatile but technically challenging colour to achieve. We know that Naples yellow (lead antimonate) was employed as the pigment of choice, but questions still remain as to how exactly it was manufactured and what recipes were followed to achieve the many shades of yellow that we can see on artwork.

To answer these questions, we first replicated a number of Naples yellows according to recipes from well-known Italian Renaissance treatises. The resulting colours span from pale yellow to dark orange and confirm that small adjustments to the recipe provided artists with an extensive palette, accommodating their chromatic needs. Then, we painted our experimental pigments on test tiles, over a white background, to assess the influence that the glazing process had on the colour. All our experiments were analysed for their chemical, molecular and chromatic profiles. Finally, by comparing and contrasting our data with data obtained from historical azulejos, we selected three Naples yellow recipes as the most representative of the Portuguese tradition.

We argue how the combination of scientific analyses and experimental replications offers key insights on artistic practices and technological choices, filling the gap left by the absence of textual evidence. Our results reaffirm the importance of technical art history as a cross-disciplinary approach to the study and preservation of cultural heritage.

The chromatic palette of Portuguese azulejos reached a peak during the 17th century. Chemical analyses have shown that Naples Yellow (lead antimonate) was the pigment employed in azulejos, but questions remain as to its technology. Using recipes from Renaissance treatises on painting and glazing, we replicated several Naples Yellows containing various types of additives. The resulting colours range from pale yellow to dark orange and confirm that artists could count on an extensive palette by tweaking the recipes (e.g. firing temperature or fluxing agent). The experimental outcomes give us insights into the artistic process that gave rise to the range of yellows witnessed in Portuguese azulejos while putting new questions on the table. The results also reaffirm the importance of technical art history as a material-centred, holistic approach to studying and preserving cultural heritage.

The chromatic palette of Portuguese azulejos reached a peak during the 17th century. Chemical analyses have shown that Naples Yellow (lead antimonate) was the pigment employed in azulejos, but questions remain as to its technology. Using recipes from Renaissance treatises on painting and glazing, we replicated several Naples Yellows containing various types of additives. The resulting colours range from pale yellow to dark orange and confirm that artists could count on an extensive palette by tweaking the recipes (e.g. firing temperature or fluxing agent). The experimental outcomes give us insights into the artistic process that gave rise to the range of yellows witnessed in Portuguese azulejos while putting new questions on the table. The results also reaffirm the importance of technical art history as a material-centred, holistic approach to studying and preserving cultural heritage.

In this seminar dedicated to the PhD students of the CORES program, but open to the public, we shared the many questions that we are trying to answer in our project while telling the history of the chromatic evolution of the Portuguese azulejo.

In the 75th AzLab conference, three members of the ChromAz team present the project, its goals, and the results obtained so far. 

Tin-opacification of ceramics are believed to have started around the turn of the 9th century AD in today’s Iraq. It is also believed that this invention was an attempt to imitate porcelain [1]. Similarly, in the mid-15th century, it was the arrival of Chinese porcelain that inspired the Venetian glassmakers to produce white blown-glass objects, which were initially called porcellano [2]. For centuries, white glazes and glass have been associated with luxury objects.

To produce glazes, glass, and enamels, empirical knowledge initially surpassed the theoretical one. The “secrets of the trade” were learned by observing and practicing, and were mostly kept within families and passed through generations. Fortunately, some processes were written down and we can find historical recipes of tin-opacified glass materials dated as early as the 11th century AD [3]. In this work, important sources such as Abu’l Qasim’s Persian treatise on tin-glazed ceramics (14th century), Neri’s Italian treatise on glass L’Arte Vetraria (1612), Piccopalsso’s famous treatise on majolica (“The three books of the potter’s art”, ca. 1557), or Kunckel’s Ars Vitraria Experimentalis (Germany, 1679), will be addressed.

This study will gather and compare historical sources on the production of tin-opacified glass-based materials, addressing the technological transfer process among different arts – glass, enamels, glazes, and mosaic – from the 11th to the 18th century.

[1] Tite, M.S. (2009). The production technology of Italian maiolica: a reassessment, Journal of Archaeological Science, 36: 2065–2080.

[2] Verità, M., Zecchin, S., & Tesser, E. (2018). Venetian filigree glass along the centuries: Some technological  considerations. Study Days on Venetian Glass: Venetian Filigrana Glass through the Centuries, 176-I: 1-12.

[3] Holakooei, P. (2013). Technological study of the seventeenth century haft rang tiles in Iran with a comparative view to the cuerda seca tiles in Spain [PhD Thesis]. Università degli Studi di Ferrara.