I often stumble on free African Art Ebooks, dealers catalogs, and old books that are free to download. Members enjoy downloading and reading books from Lieutenant-General Pitt Rivers,
The first half is an historical introduction; the second is a collection of black and white photos of African sculpture and masks.
Dans la boucle du Congo; la sculpture africaine et son destin Belgian book mostly illustrated with objects from the Tervueren Museum, but also modern african art inspired by missionaries and with some french text of Louis Van den Bossche and done with the help of Maesen
THE CONGO AND COASTS OF AFRICA BY RICHARD HARDING DAVIS- 1907 (not very interesting)
Belgian Congo At War Read Online (1942) A coffee-table book style pamphlet with many photographs.