Not everyone believes in the adage, "out with old and in with the new." In fact, some folks want to make their new items look older by making them look rusted. A rusty exterior can give an object a weathered look, which may be complementary in certain decors Rusting can also make an item look like an antique. Whatever the reasoning for wanting to give an object a faux rusted appearance, you can do so with a bit of paint and a paint brush.
Dip the end of your small paintbrush into a container of rust-coloured paint. Dab the paintbrush onto the object to create small patches or dots. Leave space in between each blot.
Swipe a dry brush over the paint quickly and firmly just before it dries. Your goal is to push the paint around a bit. Doing so will create a graduation between the object's original colour and the rust colour.
Dip your paintbrush into another shade of brown, blotting the paint on with the same technique you used to apply the initial colour. Apply the paint to the unpainted areas. Brush the paint with a dry brush just before it dries. Continue this process with other colours that are similar to those you are using until the entire surface is painted and has achieved the look you desire.
Paint the object a base colour in whatever shade you would like before adding the rust effects, if desired. Flat or matt paints typically work best for the rust effect. Not all rusts are brown, in fact, some are orange or green depending on what weather conditions they have been exposed to. Use your imagination when deciding which colours to use for your rust effect.