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.

天竺葵湖是曙红衍生的一种有机色素，梵高和他的同时代人都高度采用。在众多印象派后代杰作中都观察到它的难以捉摸的行为，对于保护者和遗产科学家来说，目前都令人担忧。在这里，已经通过紫外可见光谱技术和HPLC-DAD-HRMS研究了天竺葵湖在油基质中的耐光性，其最终目的是了解其显着漂白的降解机理。已经对基于铅曙红的湖泊制备的油漆模型进行了单色/多色光照射的加速光老化实验，该模型是根据现有历史配方为此目的内部合成的，单独使用或与不同的白色颜料混合使用，即：氧化锌和碱性碳酸铅。老化实验不仅再现了天竺葵湖的逃亡性质，而且还证明了在曝光的初期阶段具有可逆行为。在单色溶液以及简化的曙红-油体系溶液中成功进行的针对性实验，以及关于x吨染料光物理的广泛文献的证实，使我们能够基于发挥的关键作用，提出基于曙红的湖泊的合理褪色机制。亚麻籽油和环境氧气。