Cotton textiles from the Andean site of Huaca Prieta were decorated with the world’s earliest identified use of indigo blue.

In this paper, the potential of confocal microfluorescence spectroscopy is explored for the characterization of selected red lake pigments and paints based on alizarin, purpurin and eosin (weak, medium and strong emitters). The anthraquinone pigments have been used since ancient times by artists, and eosin lakes were used by impressionist painters. Reconstructions of artists paints based on 19th century recipes are examined. The paints were made using the lake pigments bound in a range of binding media including gum arabic, collagen, a vinyl emulsion and linseed oil. The acquisition of the spectra is rapid, with high spatial resolution and the data reliable and reproducible. Together with full emission spectra, it was possible to acquire well-resolved excitation spectra for purpurin, alizarin and eosin based colors. The present investigation suggests that micro-emission fluorescence can also be used as a semi-quantitative method for madder lake pigments, enabling the determination of purpurin lake ratio in a mixture of purpurin and alizarin, which is important for provenance studies. The data obtained with microfluorescence emission with those acquired with fiber-optic fluorimetry are compared. The spatial resolution used, 8 m, is appropriate for the analysis of individual pigments particles or aggregates in a paint film. Micro-emission molecular fluorescence proved to be a promising analytical tool to identify the presence of selected red lake pigments combined with a range of binding media.

The mechanisms of red lead degradation were studied in a medieval Portuguese codex, Lorvão Apocalypse (1189), by Raman microscopy (µ-Raman) and micro-X-ray diffraction (µ-XRD). The range of pigments found for the illuminations is mainly limited to vermilion, orpiment and red lead. Micro-Fourier transform infrared spectroscopy (µ-FTIR) determined that the pigments were applied in a proteinaceous binding medium. In the red and orange colours, arsenic (As) was determined, by micro-energy dispersive X-ray fluorescence (µ-EDXRF), to be ranging 1-4% (wt %). For those colours, lead white and calcium carbonate were found as fillers whereas orpiment was applied as a pure pigment. Raman microscopy identified, unequivocally, the degradation product of red lead as galena [lead (II) sulphide, PbS].To determine the main factors affecting red lead degradation, a set of accelerating ageing experiments was designed to assess the influence of extenders and of the two other pigments, vermilion and orpiment. The experiments were followed by µ-Raman, µ-EDXRF and XRD. Raman microscopy results for the simulation of degradation of red lead, in the presence of orpiment, are in agreement to what was found in the Lorvão Apocalypse, galena being the main degradation product; also in common is a Raman band at ca. 810 cm −1 , which was attributed to a lead arsenate compound. It was concluded that in Lorvão Apocalypse, the degradation of red lead was a result of its reaction with orpiment.

Color is an important component in the perception of beauty and in an artist's original intent when creating a work. Better conservation of our cultural heritage requires detailed knowledge of artwork materials and the complex evolution they have endured over time. Organic dyes have been used from ancient times, and their characterization is a challenge that has been successfully addressed over the past few years by the development of advanced techniques, such as microspectrofluorimetry. In this Account, we describe the application of microspectrofluorimetry to the study of medieval illuminations, paint cross sections, millenary textiles, and wall paintings. In our research into color in medieval Portuguese illuminations, we chose to emphasize the importance of the experimental design and the use of microspectrofluorimetry in the context of other analytical techniques, such as microFTIR, microRaman, and micro-X-ray fluorescence (microXRF). Within this framework, we were able to unveil the full complexity of a medieval colorant and to address issues not yet explored, such as the influence of Arab, Jewish, and Christian cultures on the production and underlying technology of Portuguese illuminations. The analysis of individual pigment particles or aggregates (by excitation with an 8 mum diameter spot) in paint cross sections from works by Vincent van Gogh and Lucien Pissarro highlights the technique's advantage of high spatial resolution. Its high spectral resolution proved to be useful not only for better characterizing the dyes used to color Andean textiles but also for detecting mixtures of relevant chromophores; the emission signals for the reds in Paracas and Nasca textiles were shown to be due to the presence of purpurin and pseudopurpurin. Finally, the complexity of the study of yellow dyes and the importance of accurate historical reproductions is addressed in a study of Asian organic colorants on historic Chinese wall paintings. Microspectrofluorimetry offers high sensitivity, selectivity, fast data acquisition, good spatial resolution, and the possibility of in-depth profiling. It has proved to be an invaluable analytical tool in identifying dyes and lake pigments in works of art. As Saint-Exupéry's protagonist said in Le Petit Prince, "L'essentiel est invisible pour les yeux," or "What is essential is invisible to the eye"--but it may be unveiled with kind love, a prepared mind, and a little help from microspectrofluorimetry.