I do not see an Instructable using this method so I will share with you what I did.
I WANTED one of those WereWolf Trophy Heads that were built in another Instructable SO I began to look for the materials. The main item, the thing the trophy head IS built around was a Bear Head Taxidermi Form. First problem, there is no local Taxidermi store. Ok so I went on line, in the six months I looked, I found two offered for sale on EBay. Next problem, the one I REALLY wanted, an open mouth version sold for over sixty dollars! I got the second one, a closed mouth version, in rough shape for just over twenty-five dollars. I still wanted my Trophy Head to have an open mouth so I would have had to modify the head form. One of my motos gave rise to the second problem, "Those that CAN, DO! Those that CAN'T, TEACH and, those that CAN'T TEACH, ADMINISTRATE! AND if you have friends like mine, MOST of them fall into the teacher or administrator catagory! SO soon after you show them your latest creation, THEY want you to make them one, usually for free! Not wanting to have to find another head form OR spend a LOT of money on it, I needed a way to make a cheap copy. Figuring to use a can of expanding foam insulation, here is how I solved the problem.
The first step is standard Paper Mache, cut or tear newsprint into short strips.
Second, the strips are soaked in water, ONLY water, until they are soft but still hold together. Using one strip at a time, working the wet paper into details, the "Master" is completely covered. This layer of paper forms a sort of mold release. While the first layer is still wet, if you let it dry it will peel off just like skin after a bad sunburn, begin applying a second layer of paper that has had glue applied to it. I use Universal Border Paste which is just plain white glue but I imagine wall paper paste would work just as well. Again I make sure to work the paper into the details. Because the Paper Mache is just a one time mold, I stopped at just the two layers of paper to save time.
When the glue had time to dry, I cut open the paper (usually down the seam line) enough so I could ease the master out. I then repaired the cuts I made by reinforcing them with blue painter's tape on the inside and some more paper mache strips on the outside. A note here, later I found the spray foam does not stick well to the blue tape so applying a layer of it to the entire inside of the mold would help in the final step.
I learned through experence that the expanding foam can and will explode the mold so to make sure it would NOT, after the repairs were completely dry a applied a layer of clear packing tape. I did not need to be neat, I planed to remove it as soon as the foam stopped expanding.
Finally, starting as deep into the mold as I can reach I filled the mold about half full of foam and left it to expand. After the foam had time to expand and harden completely I peeled off the paper mold or as much as I could.
The pictures show (1) the masters, (2) the copies still in the paper molds, (3) both masters and unmolded copies and (4) masters and copies.