Answer: Teeth

There was a custom in Japan (and throughout southeast Asia) that Westerners of the day found rather curious: Ohaguro. Ohaguro, literally iron drink, was a social ritual that involved drinking a very strong iron-laced tea made from vinegar, tannins, and iron powders.

This mixture was “painted” onto the surfaces of the teeth and dyed them a very dark color with a shiny appearance. The darkened teeth were considered a status symbol in Japan and neighboring countries up until the 19th century and was still practiced by older women into the early 20th century.

What’s most curious about the whole process is that despite being done for purely cosmetic/social reasons, the process was actually very beneficial. The mixture coated and sealed the teeth in a fashion much similar to modern dental sealants and, as such, the aristocrats had lower levels of dental decay than found in the general population.