When it comes to metal objects of all kinds, there's a clear visual difference between something old and something new. Signs of aging in metal range from dents to tarnish to plain old wear-and-tear in the shine. If you need to create an artificial aged look, whether it's for theatrical purposes or your own personal aesthetic reasons, recreate these common signs of aging through both natural and artistic means. This way, you can create the same visual effect in minutes that might otherwise take years.
One of the most telling differences between new and antique metals is the quality of the sheen. Over time, shiny mirror surfaces wear down to dull, powdery ones. Recreate this effect in short order by rubbing the metal with a fine sandpaper to scratch its surface. Bear in mind that the greatest amount of wear will be visible on surfaces that are handled and come into contact with other objects, so if there are portions of the item that aren't as easily accessible, rub these less.
Give the metal an accelerated tarnish by helping to stimulate the conditions necessary for creating natural tarnish. Tarnish happens when metal is exposed to moisture and oxygen, including moisture in the air. Get the metal wet, especially with salt water, and store it in a moist environment, such as a room with little ventilation or a sealed container. This process will create a layer of tarnish in a matter of days, with speed dependent on how moist the environment stays. If the metal is galvanized, however, you will first need to rub it with some steel wool or sandpaper to remove the anti-rust coating.
If you want to give some iron or steel a rusty look without really rusting it (often a good idea for very thin metals), apply real rust powder from other metals. Purchase rust (iron oxide powder) from ceramic supply retailers and sprinkle it over some metal after coating with spray adhesive. You can remove this effect later by rubbing the area with a lacquer remover.
Part of giving an aged look to any piece of metal that's been regularly moved and transported (such as a bicycle or suit of armor) is re-creating the dents and dings that will occasionally occur in real life. Use a ball peen hammer for controlled placement of small dents, or strike large, thin pieces of metal with a rubber mallet.
Blacking metals is the process of rubbing a black dye or paint into cracks and crevices to simulate accumulated tarnish. The best type of dye to use for this is one specially formulated for this purpose, sold in craft stores for use in . In a pinch, however, you can also use black acrylic paint. Rub the blacking all over the item, then wipe away with a cloth. The cloth will remove the black from all but the areas where you want it.