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http://polygonblog.com/

www.cedarseed.com/fire/handstut.jpg

This is the online tutorial that I followed to make my masks; as I made them I realized that she left a few things out, o I had to ad lib and thus far the biggest one is, before you add the leather dye it's best to use a 'leather deglazer' and add the dye while it's still damp from that.

Enjoy!

Part 1: Sketching, cutting out, carving, and baking the mask
Step 2: Dyeing, painting, and sealing the mask

I also looked at many other leather advice columns and resources, but this is the most straightforward one from the most reliable source for start-to-finish mask making. If you're interested in leather, stamp-tutorials are also very helpful for understanding grain, thickness, etc.