Remember that set of Matisse backs owned by the Burnett Foundation that was put up for sale privately through Sotheby’s shortly after Christie’s made $48m for an example Back IV:

Sotheby’s is announcing that it will auction the four works separately — in chronological order — over the next year, starting with the earliest and most classical of them all, “Back I,’’ which will be included in its Impressionist and modern art auction in New York on Nov. 2. It is estimated to bring $20 million to $30 million.

Matisse Sculptures to Be Auctioned (ArtsBeat/New York Times)