The main altarpiece of the Old Cathedral of Coimbra (Portugal)

This paper surveys gilding methods and materials found in the original polychromy and three subsequent coatings applied to the main altarpiece of the Old Cathedral of Coimbra, between 1502 and 1900. Twenty samples from gilded surfaces were examined with optical and scanning electron microscopy for leaf thickness, and analyzed with energy-dispersive X-ray spectroscopy for alloy composition (semi-quantitative evaluation). By crosschecking the documentary data (archives and technical sources) with the analytical data, the results point out several aspects: 1) two recurrent techniques can be distinguished: water-based burnished gilding on bole, and oil-based matte gilding on mordant; 2) gold leaf thickness is clearly below one micron over time; 3) in 1502, 1583 and 1685, the hand-beaten gold corresponds to the highest grade of the metal (up to 23 carat gold). This degree of fineness corresponds to the required purity and its transcendental meaning in the religious context in which the precious metal was used. In 1900, the ternary alloy found, equivalent to 20 carat gold, is more pertinent with the restoration then carried out and perhaps with the need to save money. Research on the concentrations of characteristic trace elements present in the gold alloys is being pursued.Le retable majeur de la Sé Velha de Coimbra a fait l’objet de quatre revêtements polychromes, parfaitement datés, de 1502 à 1900. Les dorures qui les caractérisent ont été étudiées à partir de vingt prélèvements, pour évaluer l’épaisseur des feuilles d’or (microscopie optique et électronique à balayage), la nature et la composition des alliages d’or (spectroscopie de rayons X à dispersion d’énergie). En croisant l’ensemble des données historiques, techniques et analytiques, il est possible de tirer plusieurs conclusions : 1) deux techniques de dorure sont récurrentes : la dorure brunie, à l’eau et appliquée sur bol, et la dorure mate, à l’huile et appliquée sur « or de couleur » ; 2) l’épaisseur des feuilles d’or est nettement inférieure au micron quelle que soit l’époque considérée  ; 3) en 1502, 1583 et 1685, l’or battu est fin, supérieur à un or 23 carats. Ce titre est parfaitement en accord avec la pureté que l’on attendait alors du précieux métal et l’expression de transcendance dont celui-ci était le symbole. En 1900, l’alliage ternaire employé, à peu près équivalent à un or 20 carats, répond davantage aux besoins de la restauration entreprise à cette date et, peut-être, à un souci d’économie. Une recherche sur la concentration des éléments traces, caractéristiques de l’or suivant sa provenance, est en cours

Calcium sulfate fillers and binders in Portuguese 15th and 16th centuries: Ground layers from a family painting workshop — Study by multianalytical spectroscopic techniques

This study presents results on a developed methodology to characterize ground layers in Portuguese workshops. In this work a set of altarpieces of the 15th and 16th centuries, assigned to Coimbra painting workshop was studied, overall the masters Vicente Gil (doc. Coimbra 1498–1525), Manuel Vicente (doc. Coimbra 1521–1530) and Bernardo Manuel (act. c. 1559–94), father, son and grandson, encompassing from late gothic to mannerist periods. The aim of the study is to compare ground layers, fillers and binders of Coimbra workshop, and to correlate their characteristics to understand the technical evolution of this family of painters, using complementary microscopic techniques. The cross-sections from the groups of paintings were examined by optical microscopy and the results were integrated through the analysis obtained by μ-X–ray diffraction, scanning electron microscopy with energy dispersive X–ray Spectrometry, μ-confocal Raman and occasionally with μ-Fourier transform infrared spectroscopy imaging. Ground layers are of calcium sulfate, present as gesso grosso (mainly anhydrite with small amounts of gypsum) in the first and last phases of the workshop and gesso mate (mainly gypsum with small amounts of anhydrite) in an intermediate period. Binders have protein and oleic characteristics

Análise por fluorescência de raios X de duas moedas e uma fivela medievais do Buraco da Moura de São Romão

International audienc

Subsídios para o estudo do Bronze pleno na Estremadura atlântica: análise por fluorescência de raios X de materiais metálicos do sítio das Baútas

International audienc

Plantas Tintureiras Dye Plants

Existe uma vasta bibliografia, até ao séc. XVIII, sobre plantas produtoras de corantes naturais, sendo que apenas um número limitado foi utilizado no tingimento de têxteis antigos, devido à capacidade de resistência à lavagem e ao desvanecimento. O cultivo de plantas ou a sua existência no mundo silvestre tiveram uma enorme importância sócio-económica para muitas comunidades espalhadas pelo mundo e pelas intensas trocas comerciais que geraram. A extracção dos corantes era feita a partir de diferentes partes de plantas ou árvores. Nalgumas plantas eram utilizadas as folhas, enquanto noutras se aproveitavam as flores, as raízes, os frutos, troncos ou sementes. Os corantes podiam ser extraídos através de processos complexos que envolviam diversas operações como maceração, destilação, fermentação, decantação, precipitação, filtração, etc. Neste âmbito, são apresentadas algumas das plantas cultivadas em Portugal e em muitos outros países europeus e que foram usadas em tinturaria. Este trabalho pretende ser um contributo para obstar à perda de conhecimentos das condições de cultivo e da forma como se maximizava a produção de corantes.A vast bibliography exists, until the 18th cen-tury, on natural dyes obtained from plants, but only one limited number was used in the dyeing of old textiles, due to capacity of resistance to wash and light fading. The culture of plants or its existence in the wild world had an enormous economical importance for many communities spread for the world, and the intense commercial exchanges that had generated. The extraction of dyes was done from different parts of plants or trees. In some plants was used the leaves, others, only the roots, the fruits, trunks or seeds. The dyes could be extracted through complex processes that involved various operations as maceration, distillation, fermentation, decantation, precipitation, filtration, etc. In this scope, some of the plants cultivated in Portugal are presented and in many other European countries and that they had been used on dyeing. This work intends to contribute to the loss knowledge of the conditions of culture and to the form of how it was maximized the production of dyes

DATA MINING ANALYSIS OVER A DATABASE OF MATERIALS OF PORTUGUESE PAINTINGS FROM THE 15TH AND 16TH CENTURIES

This paper explores laboratory analyses of ground layers of Portuguese wooden painted panels of the 15th and 16th centuries, performed in the Laboratório de Conservação e Restauro José de Figueiredo – Instituto dos Museus e da Conservação. Based on this information, a database of materials was built. A subset of the database was selected to perform a data mining analysis. We used a method based on decision tree learning, Fisher’s exact test and permutation testing and it was possible to find a ground layer technique that distinguishes António Nogueira’s Ferreira do Alentejo retable from other paintings in our database. This constitutes a small contribution to a better understanding of Portuguese painting since it was possible to establish that António Nogueira used coloured ground layers, which was an emerging technique at the time. Another contribution of this work is to show that the methodology we present here can be applied to other case studies based on similar data

REDISCOVERING THE ARRAIOLOS TAPESTRIES - ANALYSIS OF NATURAL DYES AND FIBERS IN HISTORICAL SAMPLES

Arraiolos tapestries are probably one of the richest artistic Portuguese expressions in terms of textile heritage. It is difficult to date the beginning of the production of rugs in Arraiolos, but they were already produced in the late 1600’s as they are listed in the inventories of Portuguese aristocratic households in the beginning of the 18th century. This study is integrated in project “REMATAR- Rediscovering the Materials of Arraiolos Tapestries” (PTDC/HAH/64045/2006) which intends to obtain systematized information on the composition, structure and degradation processes of these tapestries, and to use this data to improve conservation methodologies. The gathered data on natural dyes and mordants used in tapestries dated from different periods will hopefully allow the establishment of a time scale of materials usage. The tapestries studied belong to the Museu Nacional de Arte Antiga (MNAA) which the most complete and representative Arraiolos collection. Wool, linen and hemp were the most important fibres used in the making of Arraiolos tapestries. The richness of colours displayed by some of the Arraiolos tapestries denotes the likely use of a wide variety of dyes. However, only a few dye sources used worldwide to dye wool are described in the few bibliographic reports on Arraiolos making. Dye identification is usually done by extraction of the dyed fibre followed by high performance liquid chromatography with diode array detection (LC-DAD) and coupled with mass spectrometry (LC-MS) analysis of the extract. Scanning electronic microscopy (SEM), techniques enable the comparison of the fibers length, thickness, cross section and surface analysis. SEM combined with energy-dispersive x-ray analysis (EDX) can be used to give information on degradation processes and also on the mordants. Several procedures are available in the literature to extract dyes from wool and a study was performed to evaluate which is the most adequate for the different classes of natural dyes. Samples taken from a 17th century rug (nr 88 from the MNAA collection, dimensions 294x168cm) were extracted using optimized developed extraction procedures and analyzed by LC-DAD and LC-DAD-MS in order to identify the natural dyes. Microanalysis by SEM-EDX and μ-PIXE was done to identify the fibres used and assess their degradation; mordant analysis was done by 2D elemental mapping. The results on the historic samples show that hemp and linnen were used for the support (warp threads) and wool for the weaving. Weld (for the yellows and greens), indigo (for the blues and greens) and cochineal (for the reads) were used to dye the wool fibres. Cochineal dye was never referred by Rivara in his reference dye recipe book probably because it describes the Arraiolos manufacture in later periods, when tapestries had lost richness of patterns and colours. In general, the wool fibres display the typical scale structure of wool with no obvious disruptions of morphology. However, in some cases, the wool fibres present roughened surfaces with loss of scale structure, transversal cracking and longitudinal splitting which is indicative of wear and biological degradation. With exception to blue dyed fibres, EDX analysis showed the presence of aluminium (and, in some cases, other metallic minor elements) evenly distributed over the fibres which is consistent to the use of alum as mordant

Rediscovering the materials of Arraiolos historical tapestries: fibre and mordant analysis by SEM-EDX and μ-PIXE

Arraiolos tapestries are probably one of the richest artistic Portuguese expressions in terms of textile heritage. It is difficult to date the beginning of the production of rugs in Arraiolos (Southern Portugal), but they were already produced in the late 1600’s as they are listed in the inventories of Portuguese aristocratic households in the beginning of the 18th century. In this work, we present preliminary results of microanalysis by SEM-EDX and μ-PIXE of fibres from Arraiolos rugs of the Ancient Art National Museum collection in order to assess fibre identification and degradation evaluation and mordant analysis by 2D elemental mapping. This study is integrated in project “REMATAR- Rediscovering the Materials of Arraiolos Tapestries” which intends to obtain detailed and systematised information on the composition and structure of these tapestries and on their degradation processes and to use these data to improve conservation methodologies. Moreover, the collected data on the dyestuffs and mordants will hopefully allow a time scale of materials usage that could assist on the dating of other Arraiolos pieces. The results on the historic samples show that linen and hemp were used for the support (warp threads) and wool for the weaving. In general, the wool fibres display the typical scale structure of wool with no obvious disruptions of morphology. However, in some cases, the wool fibres present roughened surfaces with loss of scales structure, transversal cracking and longitudinal splitting which is indicative of wear and biological degradation. With exception to blue dyed fibres, EDX analysis showed the presence of aluminium (and, in some cases, other metallic minor elements) evenly distributed over the fibres which is consistent with the usage of alum as mordant. Further quantitative analysis is ongoing to ascertain the elements source and identification of the mordants used

Rediscovering the materials of Arraiolos tapestries: fibre and mordant analysis by SEM-EDX and μ-PIXE

Arraiolos tapestries are probably one of the richest artistic Portuguese expressions in terms of textile heritage. It is difficult to date the beginning of the production of rugs in Arraiolos (Southern Portugal), but they were already produced in the late 1600’s as they are listed in the inventories of Portuguese aristocratic households in the beginning of the 18th century. Sensitive detection techniques play an increasing role in the chemical investigation of historical objects since the knowledge derived from the chemical composition of materials is of upmost importance for textile conservation and restoration purposes.In this work we present results of microanalysis by SEM-EDS and μ-PIXE of fibres from Arraiolos rugs (Rug nr. 88, from the 17th century) of the Portuguese Ancient Art National Museum collection (MNAA)