Here’s what caused black stains on Leonardo da Vinci’s Codex Atlanticus

The culprit: nanoparticles of metacinnabar, a mercury sulphide black crystalline phase.

https://arstechnica.com/science/2023/05/heres-what-caused-black-stains-on-leonardo-da-vincis-codex-atlanticus/?utm_brand=arstechnica&utm_social-type=owned&utm_source=mastodon&utm_medium=social