Now comes the tricky part! you have to cover the clay with a substance named Rebound 25 from Smooth-on, by using a brush to carefully lay down the first layer to capture the detail then wait and apply the next layer, each one a thicker layer than the one before. There needs to be a total of 4 layers. (This is that pink stuff you see under that rough white surface. Then once that dries you apply the Plasti Paste (the white stuff) over it this is only to support the shape of the Rebound 25 as it is very flexible. This takes an hour or so to dry. I did the upper and lover parts separate due to the large fangs. Also make sure you put "keys" into the outher layer of the Rebound 25, this is to hold the layer into position properly during casting. Do this before applying the Plasti Paste!

This is essentially what I bought to make this mask.
http://www.dickblick.com/items/34106-2009/