This entry describes masking as a general practice and stops short of a great deal, deliberately. The reasons are worth stating rather than leaving as an apparent gap.
Masks are among the most heavily restricted objects in the traditions that use them. The restrictions are not uniform and they are not vague: particular masks may be seen only by initiates, or only by one gender, or only at one point in a ceremonial year; particular masks may be made only by named people; some may not be photographed, and some may not be described to outsiders at all. In several traditions the masked figure is not understood to represent a being but to be one for the duration, which is why the language of costume, character and performance imports assumptions that do not hold.
Masks are also among the most heavily removed objects. Museum collections worldwide hold ceremonial masks taken during suppression campaigns, purchased from people who had no right to sell them, or acquired without any record at all. The Hopi Tribe has objected formally and repeatedly to the auction of katsina friends in Paris, arguing that they are not property and cannot be sold by anyone. The Pueblo of Zuni has pursued the return of Ahayu:da with substantial success, on the ground that they belong to the community as a whole and no individual could ever have alienated them.
The reasoning applied elsewhere in this atlas applies here. That material about a restricted mask is already published, already in a museum catalogue, or already photographed does not clear it for republication. Availability is not permission, and the fact that an earlier wrong has been committed is not an argument for repeating it.
Anyone wanting the particulars of a given tradition's masks should be asking that tradition, which will answer or decline. Both answers are theirs to give.
Sources The Return of the Ahayu:da: Lessons for Repatriation from Zuni Pueblo and the Smithsonian InstitutionWilliam L. Merrill, Edmund J. Ladd and T. J. Ferguson with Hopi Masks: Hopi Tribe v. Neret-Minet and Estimations and Ventes aux Encheres (Art-Law Centre case note)Art-Law Centre, University of Geneva