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Organic colorants based on lac dye and brazilwood as markers for a chronology and geography of medieval scriptoria
Publication . Nabais, Paula; Melo, Maria J.; Lopes, João A.; Vieira, Márcia; Castro, Rita; Romani, Aldo; DCR - Departamento de Conservação e Restauro; LAQV@REQUIMTE; SpringerOpen
This work presents the first proof of concept for the use of molecular fluorescence signatures in medieval colours based on lac dye and brazilwood lake pigments. These two important medieval dyes were tested as markers using their UV–Visible emission and excitation spectra. These medieval paints had been previously fully characterized through a multi-analytical approach. In this work, molecular fluorescence spectra were acquired in manuscripts dating from 12th to 15th c., which were produced in monastic scriptoria or workshops. First, the spectral distribution and relative intensity of the emission and excitation spectra were discussed in detail by comparison with reference compounds, including reproductions of paints based on medieval technical texts. It was possible to group the spectra according to recipe specificities. Then, statistical methods (principal component analysis and hierarchical cluster analysis) were applied to the same fluorescence spectra and the generated clusters were compared with the previous ones. Principal component analysis was initially employed to eliminate redundancy in fluorescence data, so minimizing bias on the hierarchical cluster analysis results. Except for some misplaced spectra, the placement of samples per group was confirmed. The outliers resulted from either a poor signal to noise ratio or occurred because certain paints were unique, such as the colour produced by mixing lac dye and brazilwood, which was found in manuscripts from the Alcobaça monastic scriptorium. Previously, by using infrared or Raman spectroscopies, only lac dye could be detected. Notably, these paints compare well with a recipe that was reproduced from the text by Jean Le Begue, in which both dyes were required.[Figure not available: see fulltext.]
Microspectrofluorimetry and chemometrics for the identification of medieval lake pigments
Publication . Nabais, Paula; Melo, Maria J.; Lopes, João A.; Vitorino, Tatiana; Neves, Artur; Castro, Rita; LAQV@REQUIMTE; DCR - Departamento de Conservação e Restauro; SpringerOpen
Microspectrofluorimetry offers high sensitivity, selectivity, fast data acquisition, good spatial resolution (down to 2 μm), and the possibility of in-depth profiling. It has proved to be a powerful analytical tool in identifying dyes and lake pigments in works of art. To maximize the extraction of the information present in fluorescence emission and excitation spectra, we propose a chemometric approach to discriminate dark reds to pink colours based on brazilwood, cochineal, kermes and lac dye. These range of hues was obtained using a diverse range of medieval recipes for brazilwood, kermes and lac colourants and Winsor and Newton archive for cochineal lake pigments; the lake pigments were analyzed as colour paints (arabic-gum and glair were the medieval binders selected). Unsupervised (HCA & PCA) and supervised (SIMCA) modelling were tested, allowing to explore similarities between colourants and classify the spectral data into the different lake pigments classes. It was possible to separate the four different chromophores based on their excitation spectra or bringing together the emission and excitation spectra. The first method could also differentiate between the cochineal lake pigments, in particular between crimson lakes with different aluminates and an extender (gypsum) and between carmines with different complexing ions (aluminum and calcium).
The book on how to make all the colour paints for illuminating books: unravelling a Portuguese Hebrew illuminators’ manual
Publication . Melo, Maria J.; Castro, Rita; Nabais, Paula; Vitorino, Tatiana; LAQV@REQUIMTE; DCR - Departamento de Conservação e Restauro; SpringerOpen
The book on how to make all the colour paints for illuminating books invites readers to step inside the workshop of a fifteenth century illuminator in Portugal. This illuminator was the carrier of a tradition on how to make colours with ‘which you can illuminate or paint or capitalize or write’ that dates back, at least, to the thirteenth century. This unique knowledge and know-how was carefully preserved in Portuguese language, in Hebrew characters, in a collection of texts now known as Ms. Parma 1959 (Parma, Italy, Biblioteca Palatina, MS 1959, folios 1r–20r). Its ultimate purpose was possibly to assist on the production of Hebrew Bibles, where the precision of the text would have been illuminated by the colours described in this ‘book of all colour paints’. This medieval treatise describes the main steps and ingredients for producing painting materials, such as mosaic gold, red lead, verdigris, brazilwood lake pigments, lac dye red, vermilion, parchment glue, among others. It also instructs on the binding media that should be used to produce the colour paints. In this paper, we will discuss the technical aspects relevant for the success of the making of the painting materials and of the experimentation of this remarkable text, copied in the fifteenth century.
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Fundação para a Ciência e a Tecnologia
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SFRH
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SFRH/BD/76789/2011