I was just given a leather mask from a friend last week who had it and the piece had been sitting at her house for years.
It's old and VERY well made.  Not black.  A dark brown with thick leather.
I think that it looks fun.  But I've never tried the mask thing.  Now, though, I can! 
 
The gas mask ... one of the nastiest porn shots that I ever saw was a puppy getting fisted by a bad dragon product by his "daddy".  He was in a sex sling, bound up and was wearing a gas mask.  
The short video was nasty and hot.  Emphasis on nasty.  So I guess that it has a place in hard core play.
I'm interested in reading what others have to share!!!