Step 1: Materials and PEPAKURA!!!!!!
Thick paper/board (a4)(make sure it fits in your printer, haha)
Clear cast resin (two part)
Plaster of Paris (or if you have more budget, body filler)
Sculpting tools (I actually only used cutters, small files because I didn't have pro sculpting tools with me)
Matte spray finish
Brown and yellow water based paints (or just go get your poster color set, or watercolors.)
old worn out brush
paint thinner (depends on what paint you're using)
I'm well aware that not everybody is familiar with Pepakura and 3d modelling, so I'm making it easier for you.
Pepakura is a program that unfolds 3d models so you'll be able to make a real life papercraft model of it.
So I downloaded a model from sketchup community component models and reduced the planes for papercrafting, after then I unfolded it in Pepakura and printed it out on a thick paper. If you've never done this before, every edge of the pieces are numbered, where there's another piece that has the same number on an edge, that means they go together. there's a positive piece and a negative piece, if you can see there are flaps to some edges and to some there isn't. when you find the same numbered ones, you'll have to stick the one with a flap to the back side of the one without a flap so their edges would meet. always keep it front side up, if you get me. if you keep on reversing sides you'll just mess the model up sooner or later.
*Oh! What's that right there? A file! must be the papercraft file! Try it now will you?*
the paper is set to a4. the diameter of the helmet is about 25cm I think
Step 2: Fibreglassing!
The resin has two parts, the ratio depends on the brand you're using, so make sure you read the instructions on the container first!
Mix them in disposable plastic cups, or any plastic cup you won't use for consumption anymore ever. Don't use styro cups because the resin will dissolve it.
Now prepare a cup with acetone(CAREFUL!), to clean up your brush after using it with resin.
Mix a few ounces of resin on your plastic cup and brush a few layers on the exterior of your helmet and horns. now wait for it to dry. make sure there's no part left without resin.
(NOTE: it's better to use Aluminum foil rather than paper to dry it on, because it doesn't stick permanently to resin)
Now when the whole thing is dry, turn the helmet upside down. Cut a few pieces of fibreglass mat, maybe 2x2inches. Brush some glue, or if you have spray glue, then spray it on the inside of the helmet then cover it with fibreglass mat. Again, make sure you don't leave any part without mat.
Now mix a few more ounces of resin on your plastic cup and brush it over the insides. Now while curing, it's gonna be hot, because of the reaction of resin and fibreglass. Do not touch it. leave it for a few hours before you go to the next step. :)
*NOTE: since I can't put the fibreglass inside the horns, I just coated it with fibreglass and resin outside. It works just as fine. :)
Step 3: Sticky Sticky
Now put a little on the horns and a little on the helmet, just right where you're gonna connect the two. Dry it up a bit then stick the horns to the helmet. you can put tape around it for support so it won't get misaligned. it usually dries in 3 hours and cures fully within 8-10 hours.
now this next one is optional but i like doing it so the Plaster would have something to hold on to. Prepare some of your epoxy again and put some all over the whole helmet and dry it up for an hour. . . then on to the next step :)
Step 4: PLASTER AND SCULPT!
Now get your plastic cups again and mix water, PVA glue, and plaster. the ratio should be 1:1:2 in the same order. Then while your epoxy is a little soft, brush in the plaster mix on the whole thing. it's gonna be a little frustrating trying to make it really thick. It took me numerous layers before the thickness I wanted. don't let the plaster cure fully before you brush the next layer, because it will just crack while you're sculpting it.
Now when it's fully cured, sculpt some crack and details, it would be easier if you brush or spray water on the surface you're gonna sculpt, the plaster will be a little softer then.
Then you can use the sandpaper on the parts you think are really rough. but leave rough parts because it could add to the aged effect.
Step 5: PAINT! Part 1!!!
Then mix a few browns and yellows with water and just wash it over the horns. this way the paint will seep through the dents and would look like dirt on your horn. repeat this step until you're all good with how it looks.
Now for the "IRON" part. Paint it all black(no, not including the horns). then when it's dry, go pick up your worn out brush and brush in very light layers of silver paint. don't be too careful, just brush it randomly. Now this would give you a good "old steel" look. Don't worry about making it clean, it's supposed to look old and dirty.
now my faaaaavorite step! NEXT!
Step 6: FINISHING!
Then you can either use cotton balls, or if you're feeling sloppy, use your hands. brush a few of your paint mix around the helmet. yes, randomly. and dab the cotton on the painted parts, or your hands.
then we're there! VOILA! you now have a helmet...
woops! spray some matte finish on it first. I forgot that one. eeeek!
if you don't have any, just get your resin, I'd bet you have more than some left. and brush a thin layer over the paint. so it won't fade.
okay now we're really done. GOODLUCK!
HOPE THIS HELPED!