I put together this demo page walking them through the process along with this video.
How old is each mask?
Ivory Pendant Mask: Court of Benin. Iyoba, Nigeria
Yoruba (Ife) bronze casting of Oduduwa
Ngady aMwaash, Kuba Royal Mask, Peabody Museum, Harvard University
Creative Commons, Wikipedia Edo Ivory Mask
Public domainIFE Kings Head
Creative Commons, Wikipedia Ngady aMwaash, Kuba Royal Mask