Sand or rough up the surface lightly with 220-grit sandpaper or ultra-fine steel wool, so the paint will adhere properly.
Set the item to be finished on a plastic tarp, or mask off around it with plastic and masking tape if it is permanently attached, such as a light fixture might be. Remove screws or similar pieces, as well as glass and other non-paintable surfaces, or cover them with masking tape.
Apply a coat of spray primer to the entire area to be faux-finished. Hold the can 8 to 10 inches from the surface and move it in stroking motions, keeping the can moving, releasing the trigger at the end of each stroke. Allow the primer to dry for 30 minutes.
Spray on a coat of flat black enamel using the same spray technique. Be sure to cover all of the primer so that none of it shows through the black. Allow the black coat to dry until it is completely dry to the touch.
Apply a coat of silver spray enamel. The cheaper paint gives a more convincing matte finish. Avoid paints that are advertised as chrome repair or have very high-gloss finishes; what you need is the right look. Apply the silver sparingly so that some of the black shows through in a few places to give dark gray shadows. Work to prevent runs and drips by spraying in short bursts.
Dust the silver with a few very light strokes of black to give the feeling of the porous surface. Hold the can farther back and work in very short, stationary bursts. This will speckle the silver and add depth to the finish. Don't worry if you go too far; more silver can be added. Once you have the look you are happy with, stop.
Apply a coat of matte clear enamel spray finish over the silver to seal the finish.