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Geranium lake is an eosin-derived organic pigment highly employed by Van Gogh and his contemporaries. Its elusive behavior, observed in a large number of post-impressionism masterpieces, is of current concern for both conservators and heritage scientists. Herein, the lightfastness of Geranium lake within oil matrix has been investigated by means UV–Vis spectroscopic techniques and HPLC-DAD-HRMS with the final aim of understanding the degradation mechanism behind its marked bleaching. Accelerated photo-aging experiments irradiating with mono/polychromatic light have been carried out on oil paint models prepared with lead eosin-based lakes, in-house synthesized for this purpose according to available historical recipes, alone and in admixture with different white pigments namely, zinc oxide and basic lead carbonate. The aging experiment not only reproduced the fugitive nature of Geranium lake but also evidenced a reversible behavior during the preliminary stages of the light exposure. Succeeding targeted experiments employing monochromatic light as well as a simplified eosin-oil system in solution, corroborated by the wide literature regarding the photophysics of xanthene dyes, allowed us to propose a reasonable fading mechanism of eosin-based lakes, based on the key role played by linseed oil and environmental oxygen.

Vincent van Gogh used fugitive red lake pigments that have faded in some paintings. Mapping their distribution is key to understanding how his paintings have changed with time. While red lake pigments can be identified from microsamples, in situ identification and mapping remain challenging. This paper explores the ability of molecular fluorescence imaging spectroscopy to identify and, more importantly, map residual non-degraded red lakes. The high sensitivity of this method enabled identification of the emission spectra of eosin (tetrabromine fluorescein) lake mixed with lead or zinc white at lower concentrations than elemental X-ray fluorescence (XRF) spectroscopy used on account of bromine. The molecular fluorescence mapping of residual eosin and two carmine red lakes in van Gogh's The Olive Orchard is demonstrated and compared with XRF imaging spectroscopy. The red lakes are consistent with the composition of paint tubes known to have been used by van Gogh.

This chapter provides a description of colour changes in the Amsterdam Vase with Sunflowers due to chemical alteration of pigments, with a focus on geranium lakes and chrome yellows

This paper offers an updated review of the variety of physicochemical analysis applied so far to Levantine rock art (Spain) to characterize the composition of the pigments, as well as the substrate and/or the natural coating covering these particular prehistoric paintings. This paper is part of a broader special issue evaluating the real contribution of scientific approaches to rock art research, assessing how they have improved our understanding of this particular heritage and the new research questions they open. In this context, and with a focus on Levantine rock art, our aim is to explore: 1. The guiding principles behind the different sorts of analysis conducted and published so far; 2. The non-invasive and invasive techniques applied to answer the research questions raised, and 3. If the result published as yet have met the expectations of rock art researchers. We also reflect on the potential, the limitations and the future developments of this sort of studies, as well as on the ethics and desirable protocols of applying invasive techniques to this UNESCO World Heritage listed archaeological remain. While the focus is Levantine rock art, the discussions raised by this paper and the experiences reported in relation to the various techniques used are of global interest, especially when dealing with open-air rock art.