What is a black, preserved egg called?
The current most common term in English appears to be "century egg", but it's also been known as a thousand-year egg or hundred-year egg.

It's typically produced by aging in a solution of table salt, calcium hydroxide, and sodium carbonate, but traditional methods involved less refined versions of those chemicals wrapped in clay (and some quantity of rice bran).

More details in this Wikipedia entry.



Image: Wikipedia/Wiki commons