Roger, I've never made a mask before, but I did see a video by Cheryl Smeja entitled "Free Forming and Lasting". According to Cheryl putting vegtan in any water hotter than 150 degrees will burn the leather, and shrink it. What she does is heat the water to 120-130 degrees, and adds 1/2 to 1 cup of ammonia to 5 gallons of water. The ammonia will soften the leather, make it quite mouldable, and when it dries it's hard. She just submerges the leather into the hot water until the bubbles quit. Then she has fun with the leather making really neat things. I still like your mask tho.
Steve