A few Halloweens back I had need for a life size bright green skeleton torso (as we all do at least once in our lives.) I checked around online but the cheapest ones I could find were $30-$80, plus they looked kind of dorky. The skele was just one part of a larger decoration project so I couldn't justify spending that much on it.

I didn't have much cash on hand, but I did have some basic crafting supplies and the time to make something unique. This Instructable will detail the process of building this mean green bone machine, and my experience using drywall compound for mold making.

Materials and Tools
Acrylic Paint / Spray Paint. Plenty of black and white, and other colors of your choosing
String, general purpose
Human Skull (plastic replicas are an acceptable substitute)
Insulation foam in a can (Great Stuff)
Dry Mix Drywall Compound
Cheese Cloth / Medical Guaze
Elmer's Glue (white glue)
Hot Glue & Gun
Paint brushes, 1/2 to 2 inch wide
A plastic tub to mix the mache' in
Plastic Tarp to work over
More time than money

Step 1: Plaster Molds and Foam Skulls

I could have just used a cheap plastic skull straight from the store, but again, my budget was limited and I need a lot more skulls for other projects. I decided to make molds of a one of those cheap plastic skulls and use them to make foam replicas. The molds are made from drywall compound and cheesecloth, and the foam used is the kind that comes in a can. These foam replicas were then painted with acrylic paint and used in this project as well as other decor.

Why drywall compound instead of the traditional plaster of Paris? There are some very good reasons for this:
  • Drywall compound is cheaper than plaster
  • It isn't as dense as plaster and is easier to carve and break away unwanted bits
  • It takes longer to become completely solid giving you more time to work with it
Now I want to point out that these molds would make a professional model maker cringe and they not intended to produce perfectly detailed replicas, they are not good at it. What they are good at is being fast and cheap to make. Who cares if the details aren't perfect and there's a crack here or there, leave perfection to those with budgets and time.

As soon I was finished with the molds I threw them away, I didn't feel the slightest bit attached like I would have if I had put a ton of effort into them.

* I didn't take many pictures of my original skull molds but I am making some more this year. I will add pictures as I make progress.

Making Plaster Molds
  1. Get a plastic skull, a 12"x12"ish piece of plywood, and a bit of clay. Most any non-drying clay will do.
  2. Drill a counter hole into the bottom of the plywood and follow it with a smaller hole drilled all the way through. The second hole is only large enough to let the threads of the screw through, the larger hole lets the head of the screw sink into the wood leaving a flat bottom.
  3. Drill a hole in the bottom of the skull with an even smaller bit, the screw will need to bite into this pilot hole.
  4. Screw the skull securely to the board, tight enough that it doesn't spin.
  5. Fill the recesses and holes of the skull with clay. These undercuts would keep the skull stuck in the plaster when the two halves of the mold are separated. Although it is fun smashing a mold off of something, it isn't very productive.
  6. Build a dam of clay around the center of the skull as seen in the above images. This wall of clay will be the dividing point for the two halves of the mold. Add "keys" to one side of the damn by adding hemisphere chunks. Later on the impressions left by these keys will help align the two halves of the mold.
  7. Paint petroleum jelly over the entire surface of the skull with a paint brush (the brush will never be the same, use a disposable one.) You want a thin layer of jelly over the entire skull, try not to leave big gobs of the stuff and make sure to get into the little nooks and crannies. This jelly will keep the drywall compound from sticking to the skull
  8. Mix about a cup of dry compound with about half a cup of water in a plastic tub. For the first few layers of the mold you want the mix to be pretty runny so that it can get into the details. Mix and add water or compound until you get a consistency like pancake batter.
  9. Slap that batter on yer skull. Be as messy as you like but try not to get any over the top of the clay wall. Let the batter dry until it starts to harden and then add another layer of fresh mix. Repeat this step until the mold is about 1/4 inch thick.
  10. If you tried to pull the mold off of the skull now the drywall compound would crack into pieces, but if it is reinforced with cheese cloth it will be much stronger. Cut some pieces of cloth into squares large enough to cover the face of the skull. Dip these into some fresh drywall batter and lay them onto the top of your mold. Let this dry for a few minutes and then add another thin layer of batter. Keep adding layers of compound and cheesecloth until the mold is about 1/2 inch thick.
  11. Prep the un-mudded half of the skull by removing the clay barrier and add some little clay wedges to the side of the plaster. These will leave indentations in the mold that will make prying the halves apart much easier later.
  12. Slather the exposed skull and the drywall seam with more jelly.
  13. Repeat the drywall compound steps used to create the first half of the mold. Do not get plaster over the top of the first half of the mold or the pieces will stick together.
  14. Unscrew the skull from the board and use a flat head screwdriver to dislodge the skull from the mold. Now the chances are that it wont want to come out without a bit of persuasion. Since the mold doesn't need to be a perfect replica, it is fine to be rough with it and crack it in a few places. The better job you do of filling in the undercuts, the easier it will be to separate everything.
Foam Skulls
  1. Spread petroleum jelly on the inside of the drywall mold and strap the two sides together with rubber bands.
  2. Use a can of insulation foam to fill the mold. Start at the bottom and swirl you way up around the sides, don't put it in too thick or it will have a hard time curing. You don't really need to fill the center of the skull, but if you do give the foam around the edges an hour or so to cure and become solid first.
  3. After letting the foam solidify, take off the rubber bands and pull the mold apart. Some tugging may be needed to free the foam.
  4. I painted the skull for the skeleton white and then green, but I also made some blackened ones. To do this mix some black acrylic paint with water to this it down to a cough syrup consistency. Use a thick paintbrush to cover every single bit of the skull, inside the bubbles and cracks, everything.
  5. Mix some black and white paint together to get a dark grey and drybrush this color onto the skull by dipping the brush in paint, wiping most of the paint off on a paper towel, and then brushing it over the skull. The ridges and texture of the foam will pick up the paint.
  6. Mix a lighter shade of grey and drybrush the skull again. Repeat as much as you like. I haven't tried but I bet some red meaty skulls made with this method would look cool too.
  7. Some of the skulls I made had their bottom jaw removed with a hack-saw, you know, to mix it up a bit.
Congratulations on being a finalist in the Halloween contest!!! Can’t wait to see if you win! Good luck!
This is just wonderful! I love how the arms look. The unpainted stick-and-string stage looked really great. ^_^
Thank you :) <br>I totally agree about the stick version. If I find the time I am going to make another one completley from sticks, including the ribcage and skull.
Awesome project!!!.... Really, Great work!!!....
This is truly amazing! I admire your creativity.

About This Instructable




Bio: When I was young I took all of my toys apart just to see inside. Eventually I learned how to put them back together.
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