Clean the object and apply two coats of primer, if necessary. The primer will allow the paint to adhere properly to the piece.
Apply a thick coat of paint to the object in the color of your choice. Since rust forms on a wide variety of objects, the original color is not especially important.
Sprinkle the freshly painted object with a layer of fine sand. Don't worry if the sand doesn't cover the object evenly, as too much symmetry will make the finish appear artificial. Allow the piece to dry overnight.
Stipple the object with dark brown paint, using a stippling brush or wallpaper brush. Apply the paint at random, leaving some areas unpainted.
Apply a second stippling finish with a copper-colored paint over the unpainted areas. Feel free to allow the original paint color to show through in some places.
Spray the piece gently with water from a spray bottle to give variety to the finish.
Stipple on gray paint at random, using the color to highlight the object's texture.
Mist the object with water again. Splatter orange paint in areas where rust would naturally occur. Dab the orange paint gently with a cloth to blend slightly.
Allow the object to dry thoroughly.
Clean and prep the area to be painted. Use painter's tape and drop cloths to cover trim, flooring and furniture.
Apply an even coat of copper-toned paint. If you prefer a steel rust look, use gray paint for the first coat.
Dip a clean piece of cheesecloth lightly in a pewter-color paint. Gently dab the cloth onto the walls, making some areas darker than others. Reposition the cloth in your hand frequently to prevent the paint from having a patterned look. The areas of the base coat should still be visible after you've applied the pewter paint.
Sponge on brown paint with a damp sea sponge. If you used gray as your base coat, sponge on a brownish orange color instead. Use quick, light motions to keep the paint from becoming too concentrated in any one place. However, the overall surface will have significant color variations. Continue sponging until you achieve the desired look.
Finish with a clear top coat to protect the surface.