Note: Not ANSI or Snell approved for protection against errant meteorites, asteroids, or light sabers. Wear at own risk at being called a geek. Light sabers not your thing, maybe make this instead.
Step 1: It's Just a Shell Game...
It's a hardhat hat over a hardhat.
Pros would probably fiberglass or vacuum form this thing. No need to if you are
You will need a regular standard hardhat to build upon. Get the one with the ratchet headstrap adjuster which makes it fit real nice for a few bucks more.
You will need some cardboard and paper.
You will need a beach ball or something similar to use as a half dome form. A giant salad bowl would work too.
Black gloss paint.
Utility knife, scissors or strong shears to cut the cardboard.
Caution: Be careful with sharp things and black paint gets all over the place no matter how careful you are.
Step 2: Beginnings of a Death Star...
This is just like making a Giant Magic 8 Ball but we only need to make half a sphere.
Wrap the inflated beach ball or your giant salad bowl with plastic wrap to keep it clean from the overspilled glue.
The actual helmet is really a little flattened out at the top but just stick to the round form to make things easy. It will still look good.
Glue a band of a cardboard strip about 2 inches wide around the circumference of your sphere. This is your headband.
Note that while waiting for the glue to dry, I actually made two Dark Helmets.
You can piece together cardboard pieces to make them longer.
Glue up strips that go around the top from one side to the other.
Cross them and glue at the center. You are trying to form a spherical ribcage for the helmet. Do this as many times to leave minimal spaces between the strips. The gaps will be bridged with papier mache later.
Glue another layer or two around the headband to stiffen it up.
You can use tape or a stapler to tack the cardboard in place because it has a tendency to flex back out before the glue gets a hold.
Step 3: Nasty Ring Around the Bowl...
There is a bottom panel that flares out away from the top.
By adding and tacking on pieces in a stairstep fashion, it will end up sticking further out like the flare.
Add cardboard panels in layers. I used three strips. The transition of the rough edges will be smoothed out later with papier mache.
Trim around to get the angled side and bottom edge straight around.
Try to test fit as you go along since the length of the helmet might be too long and hit your shoulders when wearing it.
I guess if this was designed from the start, you could trace out a real curved panel in one piece to wrap the bottom portion of the helmet. This helmet was designed as I went along.
Note that I had papier mached the top just to get a sense of what it would look like filled out.
Step 4: I Need My Shades...
Glue up pieces that will act as gluing tabs for the visor edge.
Layer with more cardboard tabs to conform to the curves and transition from the sides.
Add one or two more layers of cardboard strips around to band the entire rim of the helmet to give it strength.
You can now do the final papier mache of the helmet, inside and out on the viewable surfaces.
Papier mache was just torn newspaper with a half glue/half water solution.
Let dry overnight.
Step 5: Suspension System for the Helmet.
The band should fit well around the helmet.
Since the helmet has a small rim and protrusions for its head harness system, I glued up additional cardboard bumpers for the helmet to stop against.
Glue up a crisscross band across the top of the helmet and attached to the helmet band.
When the helmet harness is dry, you can attach it to the cardboard helmet.
You will need to glue up spacer blocks to bring it up to the height of the cardboard helmet's helmet band.
Glue up cardboard spacer blocks to attach the helmet bands together. I found that three anchor points would be sufficient.
Step 6: In a Galaxy, Far, Far Away...
Like a rolling stone, paint it black.
So, if you've got nothing for Halloween, make something for nothing.
May the schwartz be with you.