New on the helmet scene here, I'm looking to do a sculpt of a helmet and I understand how to get a negative of the outside of the helmet. My confusion is in getting the positive of the helmet. Hopefully i've explained my question so that it is understandable. Any help would be great. Thanks everyone.
-Chris
Ok, to avoid confusion, first things first...
TERMINOLOGY
Your sculpt of the helmet is called the PATTERN, BUCK or just SCULPT.
What you're calling a negative is called the MOLD.
What you're calling the positive is the CASTING or PULL
CAST is the correct word for all tenses, past present and future; there is no such word as "CASTED"
Now, on to making your mold. When your sculpt is finished, and you checked it for any last minute flaws and corrected them, mix up about 300 grams of good quaility silicone and brush it on. It will try to run off and pool at the base of your sculpt, so you'll need to keep chasing it back up with your paint brush until it thickens enough to stay put. This first layer is the most important since it captures all your detail. This is called the BEAUTY COAT or LAYER.
When your beauty coat is solid enough to touch w/o coming off on your fingers, start mixing up another 300 grams of silicone and brush that on. Apply at least 4 more coats this way.
Now, find an old t-shirt and cut it up into small squares about 2" on a side.
This is where it gets MESSY. Mix up another batch of silicone, and wearing latex gloves dip the t-shirt squares into it and wet each square and work the silicone well into it and squeegie off the extra with your fingers. Then apply it to the silicone already on your sculpt. Do this until it's completely covered with the silicone soaked t-shirt squares, making sure to overlap them as you go.
When all that is dry, put one or two more coats of silicone on to smooth it all out.
You're done now with the silicone, so clean your work area, mixing spoons etc. and let that last layer cure up.
Now your mold is going to need a jacket to support it while you make your castings. There are several ways to do this- you can use plaster, plaster bandages, fiberglass (YUCK!) or you can brush up layers of resin if you have plenty to spare.
Whatever you use, you need to run a 1.5" - 2" high clay wall down the middle of the silicone, from the chin of the helmet, up and over, all the way to the bottom of the back.
Start applying your jacket material to one side of the mold, making sure that it goes up the clay wall to give you a good flange. When you're sure it will be sturdy enough, peel the clay wall away and vaseline the bejesus out of the flange on the side where the clay was, and be extra careful not to loosen your first side of the jacket while you're doing it.
Repeat the process for the other side of the jacket and let everything dry/cure for a couple hours.
Now, take a drill with a 1/4" bit and drill through both the flanges on your jacket in 3-4 places. (I usually just do 3 unless it's really big- one at the chin, one at the top of the head, and one at the bottom back.)
Take a big flat bladed screwdriver and carefully pop your jacket halves apart and set aside, you're now ready to pull your mold off your pattern. If your helmet is wide at the bottom like Boba Fett or a "300" helmet, you should be able to roll your mold off like a big rubber sock. If it has undercuts like a TIE helmet, you'll need to split the mold to get it off. Splitting it will give all your castings a small seam, but that's easily sanded off later. Try to put the split up the back in a wide area with as little detail as possible.
Now back to your jacket halves- put them back together and bolt them together with 1/4" bolts and wingnuts through the holes you drilled earlier.
dust the entire inside of your jacket with baby powder and slip your silicone mold back inside. Push and poke around inside the mold to make sure it's properly seated in the jacket.
Powder the inside of the mold now to break the surface tension of your resin and suck it into every little nook and cranny.
Your mold is now ready for it's first casting!
(But that's another lesson!)
-Sarge
