Make sure the surface you're coating is either brass, copper or bronze. If the entire object isn't composed of one of these metals, then make sure the surface you plan on finishing is at least electroplated with one of them. These metals are intrinsic to the oxidation process, in which the metals and the applied chemicals react with oxygen to provide the distinctive look of a bronze finish.
Apply lacquer remover to the metal with steel wool. (Not all surfaces will have lacquer, which is a translucent, shiny finish applied to metals, so you may be able to skip this step). Clean the metal using a mild detergent and soft cloth. Make sure you get into all the crevices to remove all the dirt. Sand down any rusted parts with sandpaper (it's unlikely you'll have rusted parts if the metal had a lacquer finish).
Apply an oxidation/patina solution. Follow the directions on the product's packaging for the exact application instructions, as these will differ from brand to brand. Generally, you'll apply an aging solution to your surface, which will begin the oxidation process.
Select the item you want to finish. Because this process does not involve oxidation, you can choose any type of solid surface, including wood or plastic.
Clean the surface thoroughly, using a mild cleanser.
Apply paint to the entire surface. Use a dark color for best results. Either spray paint or traditional paint applied with a paintbrush will work. Follow the directions on your paint product regarding drying time.
Add bronze spray paint to the surface. You can the paint directly onto the object, or you can spray the paint onto a rag and apply it by hand. Let it dry.
Apply a mixture of the dark paint used in Step 3 and water to the surface, using a rag.