Iwai Yozaemon was armorer for Tokugawa Ieyasu during the Momoyama period and was appointed official bakufu armorer when he became shōgun. His school has then been active in Nara for many decades, producing two main styles of masks, the oie-bo and the etchū-bo. This second one featured very well defined facial treats and the surface was covered with parallel lines called yasurime ("file marks"). In the Meiko Zukan there is a drawing which illustrates the main features and it is reported that this shape was the favourite of Hosokawa Sansai. On earlier masks, the nose is not detachable, while on later ones, around 1700 like this one, it can be unmounted.
Menpo for sale. Price on application.