Lamanai: Structure N9-56
"Constructed of stone rather than of stucco laid over a rudimentary armature as is generally the case elsewhere, the mask retains virtually all of its features as well as some of the 13 cm. thick coating of unusual grey stucco, created by mixing ash or ground charcoal with the plaster."
Pendergast, Journal of Field Archaeology 8:1 37-38
Note the remains of the wall in the lower front of the photograph. This is the front wall of a later temple which once covered the masks. It was removed during archaeological excavation of the site to reveal the mask beneath.