This demonstration uses sunlight to write letters on a slurry of silver nitrate and calcium carbonate, recreating an experiment dating to the early 18th century. The letters appear as light silhouettes against a dark-gray background, with the gray due to elemental silver. The demonstration is a striking illustration of the photoreduction of silver ions, the fundamental process in conventional film-based photography. This demonstration kindles the interest of beginning students in oxidation–reduction reactions.

中文翻译：

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在阳光下写作：重建历史性的实验

该演示使用阳光在硝酸银和碳酸钙的浆液上书写字母，重现了一项始于18世纪初的实验。字母在深灰色背景下以浅色轮廓出现，灰色归因于元素银。该演示非常生动地说明了银离子的光还原，这是传统基于胶片的摄影的基本过程。该演示激发了初学者对氧化还原反应的兴趣。