A while back, I bought this latex mask from BDG Sales along with an attachment for my Israeli gasmask, a rebreather bag and a flexible hose. Unfortunately, the mask was one size too large but it was on sale, so what the hey. It's a really nice mask with several panels for a nice facial contour and fit around the head.

Anyway, working with the instructions on rubberist.net I've carefully the mask apart and I've removed some of the material to make it 2 inches smaller in diameter both horizontally and vertically. Right now, I'm gluing it back together. It turns out that there's a special technique for gluing curved seams into a latex garment! Fortunately, I've sewn curved seams with a sewing machine before in regular fabric, so I was able to figure out what more or less what they were talking about.