Nok Terracottas (Metropolitan Museum of Art)
A lot of Nok artifacts have ended up in Western museums and personal collections, but the business of selling Nok artifacts to collectors is really controversial.
Here are a couple links that show what I mean.
The Rape of Nok and Kwatakwashi: the crisis in Nigerian Antiquities (University of Cambridge)
UNESCO, Nok terracotta and the Met (Elginism blog)
Nok Heads for Sale (Hamill Gallery)
