The first colour photographs were created by a process introduced by Edmond Becquerel in 1848. The nature of these photochromatic images colours motivated a debate between scientists during the XIXth century, which is still not settled. We present the results of chemical analysis (EDX, HAXPES and EXAFS) and morphology studies (SEM, STEM) aiming at explaining the optical properties of the photochromatic images (UV-visible spectroscopy and low loss EELS). We rule out the two hypotheses (pigment and interferences) that have prevailed since 1848, respectively based on variations in the oxidation degree of the compound forming the sensitized layer and periodically spaced photolytic silver planes. A study of the silver nanoparticles dispersions contained in the coloured layers showed specific localizations and sizes distributions of the nanoparticles for each colour. These results allow us to formulate a plasmonic hypothesis on the origin of the photochromatic images colours.

中文翻译：

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光谱学和电子显微镜学揭示了第一张彩色照片的起源。

第一批彩色照片是由Edmond Becquerel于1848年引入的一种工艺制成的。这些彩色图像的本质激发了十九世纪科学家之间的争论，至今仍未解决。我们介绍化学分析（EDX，HAXPES和EXAFS）和形态研究（SEM，STEM）的结果，旨在解释光致彩色图像的光学特性（紫外可见光谱和低损耗EELS）。我们分别基于形成敏化层的化合物的氧化程度和周期性间隔的光解银平面，排除了自1848年以来盛行的两个假设（色素和干扰）。对包含在有色层中的银纳米颗粒分散液的研究表明，每种颜色的纳米颗粒具有特定的定位和尺寸分布。这些结果使我们能够对光致彩色图像颜色的起源提出等离子体假设。