If you want your plastic item to look like it’s actually distressed metal, you will have to decide on whether you want to paint the item a metallic color, or if you just want to make it look like metal is only being exposed in a few places.
Covering Your Item in a Metallic Color
If you want your item to look like mostly bare metal, or if you want to create chipping or other effects that realistically expose the under layer, then you will want to cover the visible surfaces in metallic paint or another material. For maximum realism, you will usually want a highly-reflective paint or coating.
Reflective Spray Paints
Krylon makes these two spray paints that are a good value for a spray paint with an exceptionally reflective finish.
Metallic Spray Paints
Hammered Texture Spray Paint
Rub N Buff
A wax that contains metallic powder, Rub N Buff is a popular way to create very realistic metal effects. It’s available in Silver Leaf, Gold, Spanish Copper, Patina, Antique Gold, Ruby, Grecian Gold, European Gold, Ebony, Autumn Gold, Antique White, Pewter.
Chipped Paint Masking Techniques
Once you have covered your item in a metallic color, you can apply paint-chipping effects.
Latex Masking Fluid
Apply 2-3 coats of latex masking fluid where you want your chips to be. Apply paint. Remove the masking fluid to reveal the artificial chip in the paint. For a better effect, make your coats of paint thick. Leave your dried masking fluid alone, and instead, add more fluid over your first area, enlarging the area of the chip with each layer of paint. This will result in a quarry-type of effect. Changing the colors of each layer, especially between the primer and top coat, will make it more convincing. Use a pointy tool to pry up and peel your masking layers away. At the end, you can also go over the whole item with a black wash (black paint diluted with water in about a 1 to 4 ratio) to help make the steps between the layers more deep and pronounced.
Other Masking Materials
Other materials you can use to mask the chip areas are rubber cement, petroleum jelly, and mustard.
Faux Paint Patinas
The first patinas we will cover are techniques you can use for any metal or material.
Brushed-on Paint Patina
Use stippled-on flat black paint, and optionally, rust-colored paints, to your item.
Water-Masking & Spray Paint
To create a random patina pattern, use a spray bottle to spray your item. This works best on a flat item that is relatively level, because you want the beads of water to stay on your surface. Once you’ve got a generous amount of beading on your item, apply a flat black spray paint (or patina color of your choice) over the surface. Allow the water to dry, or absorb it with a paper towel after the spray paint is dry.
Reactive Metal Paints
What could be more realistic than applying actual rusted metal to your surface? Reactive metal paints are paints that contain metal flakes and can be activated to create rust or other oxidized patina effects. Check out Modern Masters iron paint.
Applying Metallics in Reverse
If you just need a few scratches and chips and want a simpler and faster approach, then you can add your exposed metal areas on top of your paint or surface, instead of creating a metallic base to paint over.
Paint Chips and Scratches
Simply take some metallic paint and use a brush to apply it with distinct edges, in mostly oval or circular shapes. Apply it to areas that would see a lot of wear, like edges and prominent features.
This is what’s called the dry brush technique. Take a flat brush and dip the very tip in your paint. Dab your brush on a paper plate until the paint is dry enough, or spread along the bristles enough, that you can paint your item with subtle brush strokes that leave the marks of your bristles. Your strokes should go back and forth lightly along edges and areas of wear. You will usually want your strokes to go in the same general direction. Don’t overdo it.
Gradual Friction Wear
For wear that looks more like years of rubbing against clothing, etc, use a tiny bit of Rub N Buff. Apply it on edges and other areas that might come into frequent contact with surroundings.