Re: Fallout 3/New Vegas "Combat Shotgun" build
I kind of got carried away with this answer. Anyone who wants to read more about shotgun stuff, you can skip this reply!
1. Where do you get the powder? Is it simply shavings from a piece of iron bar or do you find it at art supply stores?
I buy mine from a place called "The Compleat Sculptor" (yes, incorrect spelling is intentional!) They sell all sorts of fillers for resins, many I'd like to give a shot one day, but so far I've only tried a handful.
Here's their list of fillers, the metal I use is the "Iron Powder - grey (325 Mesh)"
2. How is it applied? Do you use the purple paint as glue and then sprinkle the iron powder on, or do you mix the iron powder with the paint and then apply the mixture with a paint brush?
I have tried a couple different methods, but my current favorite is to take two paintbrushes, the powder, and a cup of water to apply it. First brush is wetted down, and you brush over the area on your prop you want the rust to stick to. Take the second brush and scoop a small amount of powder onto it, then tap it lightly over the wet area to apply the powder. Wherever the piece isn't damp, the powder will fall away.
Here's a shot of a piece that's been powdered before applying the rusting agent. I also painted the parts behind the rust with a dark reddish brown, but that's a personal preference.
Just to give you an idea of what to expect when you're spraying, initially the rust powder will make a sort of nasty yellow foam. This can be immediate, like right before your eyes, but sometimes it can take a few minutes as well. This will fizzle down and settle into a nice rust texture pretty quickly (about an hour or so) but don't try to blast away this bubbling with your spray bottle! That's the chemical reaction taking place, and more accelerant will only remove the metal powder.
You can actually watch it take place in a few seconds in a video I shot of one of my Skyrim helmets being made:
>CLICK<
3. How controllable is this effect? Does the rust only appear where you applied the powder?
It can get away from you in a hurry. My advice is to start small, you can always add more after you've finished a coat, and a little powder will go a long way. I put the peroxide, vinegar and salt into a spray bottle (ratio: 4:4:1 by volume) and mist over the areas with the powder. You have to do this carefully and make sure you get a spray bottle that doesn't jet out or you'll just blast away all the meal powder.
Things will look like this after spraying. You'll have some runoff which will be tinted with the color of the rust, but if that's a problem you can always buff it off with a scotchbrite pad later. Make sure to put some scrap cardboard under your parts to avoid destroying your work surface. Oh, it will also smell like hamster pee.
I let the rust cure for 24 hours before I do anything else to it, and initially it will look pretty grisly. Once the peroxide and vinegar are gone, a lot of salt is left behind, and it's not very pretty:
A quick buff with a green scothbrite pad will get rid of this
This is a shot after the scotchbrite and after a coat of satin clear as well. This will seal the rust and it will also darken the color somewhat.
The purple paint is something I use to knock back the orange hues of the rust spots a bit and give them a bit more depth. You can see a contrast in where this has been applied (right) and left plain after clearcoat (left) in this shot. This is applied as a very damp wash using very runny paint and cleaned up with a damp paper towel. The porous surface of the rust will capture the pigment you're after on it's own.
Couple more coats of clear, and you've got some nice rusty crusty!
One word of caution, I have had issues with Krylon Matte Clear Acrylic #1311 making the rust haze over with white spots. A pass of satin acrylic clear took care of this, but satin isn't always the look you're after. If you want a matte clear, you might have to look for other paints, but I haven't tried it.
Hope this helps! Obviously not a shotgun (some Skyrim armor I made earlier this year) but same principle.
