Leather mask used by the ten decipals of sorcery in house Zau Nihl'lu'szin, with the purpouse of conceling the ten individual's faces as they get stripped of their identities at the beginning of their training. This to ensure that no one, noble or common shall be favourized by the masters and the house family and therefor have greater chances of advancing in rank.
All ten decipalswear the same clothing armor (light) and weapons to equalize them in every test and trial. If any of the 10 fortell of their identities, or even hints about it gravely enough for an outsider to recognize them they are cast out of their house.
Off course this has a great impact on the individuals and their personalities, as they must erase all ways ofbeing to seem as faceless and anonomous as possible.
Such rules offcourse invite for others to take a shot at identifying them, to either have them cast out (for leverage in sorcery ) or blackmailing.
Design was based on a mix between a kind of evil pope-hat and a armored mardi-gras
Open mouthed can be tricky as it shows more of the face than a closed one would offcourse, and make it easier to identifye the bearer, but as alot of the drow spellcasting is done merely by lipsyncing the words it had to show the lips moving (cause the clerics of Lolth has to wittness them doing it in order to grant the spell power) so it was a price to pay in the design.
Alot of drow runes engraved all around (mostly on the inside though as the mages themselves engrave their own favourite spells, and do not want to have their cover blown showing personal facts all over their faces