I finished this up awhile ago as a birthday gift for my brother/ awesome prop mask for myself. I have basically the same write up for it on my blog: boundclockprops.com. Just thought I would share it in this forum as well.
This is the mask of the evil villain Amon from the show legend of Korra.
Step 1: The Beginning
To begin with I mixed up and rolled out some Apoxie Sculpt and placed it onto the foam head with a layer of saran wrap, between the putty and the head, to keep it from sticking so I could save the head for future projects. After the initial rubbing and shaping of the Apoxie I let it cure so the really work could begin. To smooth the surface and do more shaping I applied multiple layers of bondo. After which a sequence of sanding, then bondo, then sanding some more, the bondo, then sanding, sanding, sanding, and just for good measure sanding some more.
Once the final shape came through I began making/refining the details for the mask, which for this mask was basically 5 or different parts, including the eyes, nose, mouth, the circle on top, the crown like piece around the circle, and the cheek pieces.
Step 2: Details
I started with the circle and crown pieces. To make them at first I used 1/16th inch polystyrene sheeting and cut them out on my band saw, after ruffly drawing them on a piece of paper and spray adhering said piece of paper onto the plastic. Once cut out I placed the pieces on the mask and used a heat gun to get the plastic to conform to the mask. Then I simply glued them down and used some bondo to blend them.
Needless to say the results were less than satisfactory but the ugliness doesn't stop there it got way worse as soon as i added the cheek pieces. I constructed those the same way as the previous parts. Around the same time I made my first of many attempts of making the mouth, and i decided to scrap the original sculpted nose completely and just redo it, as seen in the last picture in the sequence below.
Step 3: Redo
As the saying goes things get worse before they get better, and after making the decision to basically go back to square one and scrap the styrene parts completely things turned around and went a whole lot smother. Using the plastic piece of the crown I used more Apoxie sculpt to create the new and improved part. Instead of making the piece flat I opted to make it more of a ridge and I am very pleased with the results. I redid the cheek parts by simply using a thinner piece of plastic. (I went to home depot and bought a " For Sale" sign) The results of the remade parts were drastically better. After completing all of the remakes I glued them on and viola! the mask was in the headed in the right direction.
Step 4: Finalizing
I had cut out one eye by this point but I quickly realized the eyebrows were severely unsymmetrical which caused some problems for cutting the opposing one. After some quick refining the problem was fixed and the eyes were set which meant this project was finally coming together. I proceeded to make the circle which I made out of yet even more Apoxie sculpt, by mixing and flattening it out then taking a small plastic cup and using it like a cookie cutter stamped out the circle shape. I finished up the mask with the stipe from the circle down the nose, by taking the same plastic that used for the cheek pieces and cutting a sliver that I clued down, and shaping out the mouth which I made a stencil for and cut out with a dremel.
Step 5: Molding
Now it came time to mold the this sucker. I made three attempts to make the mold with the first two failing miserably. I used Smooth-on Rebound 25 for the first attempt but it didn't cure right. The inside was gooey and after spending the better part of an hour scraping the gunk off I made attempt number 2. This like the first one ended the same way. So I decided that the problem was most likely the primer I used was causing the silicone not to cure. Thus I coated the mask in a clear lacquer and the problem was solved. Although I had solved the issue I had run out out of Rebound 25 so I switched to Rebound 40. I applied a thin layer to capture the details followed by a thicker layer (I mixed the rubber with some thivex thickener). After the first couple layers I interlaced an open weave fabric, basically burlap, that I got for dirt cheap at Jo-anns which adds rigidity to the mold.
I finished up the mold with a mother mold made of fiberglass. After a couple layers of fiberglassing the mold was complete and ready to be peeled off for casting.
Step 6: Casting
Using Smooth-cast 65D I poured the plastic into the mold and slush cast it around. After several coats I was able to pull out the finished casting. I was able to get quite a few pulls out of the mold. i would still be able to however i accidentally ripped a piece. i have it still and i plan on repairing if i find that people would buy a copy.
Step 7: Painting
The final steps were basically to paint the mask. After a little touch up on the casting I primer the mask the sprayed on a couple layers of white paint for the case layer. After waiting for said white paint to cure I taped off the various areas for color painting. With the main colors complete the final detail was to add weathering. Which is to say "make the flaws look like they're meant to be there".
Step 8: Finished
After all was said and done I clear coated it and took some photos of it. NOTE I am not a photographer so they may not be the best, but they'll do.