Ancient Vietnamese teeth blackening

[Duncan Head]

https://www.livescience.com/archaeology/2-000-year-old-skulls-reveal-people-in-ancient-vietnam-permanently-blackened-their-teeth-a-stylish-practice-that-persists-today

Using iron salts, apparently

[Imperial Dave]

https://en.wikipedia.org/wiki/Teeth_blackening

For those like me who were intrigued by the article!