An interesting article by Souren Melikian in The New York Times (here) discusses the current state of the market for antiquities. It brings anecdotal evidence that the prices paid for antiquities continue to reflect not only the intrinsic value of the object, but the quality of its history as well. The article highlights the importance of a pre-1970 history for antiquities at recent auctions in Paris and New York. Unprovenanced objects are not selling.
The reason for this discrepancy lies in the Unesco convention adopted in 1970 to safeguard the buried heritage of mankind and shield standing monuments from looting. While many countries, including the United States, did not sign up, the convention is effectively being implemented by international institutions and, increasingly, by prudent collectors and dealers, fearful that the legitimate ownership of their acquisitions may be challenged in the future. As a result, important works of art that can be proved to have reached the market before 1970 shoot to vertiginous levels, while those that cannot fail to sell with increasing frequency.
Though this upheaval might be an indicator of things to come, the market for antiquities is of course different than the African art market. At the moment, it might be the most relevant for terracotta objects from Nigeria and Mali. Lastly, there are nuances in the quality of the documentation that establishes the presence of objects in the market prior to 1970. Private Collection, before 1970 still seems to set at rest most of the collectors (for now).