This page covers dulling and darkening metals, also referred to as antiquing. For less subtle patinas, go to the patina page.
First thing you want to do is wipe the item off with acetone, and use an abrasive pad or fine steel wool, to remove any protective coatings or oils. You might also want to wash the item with soap and hot water.
Brass, Bronze and Copper
Vinegar and Salt
Submerge your item in a mixture of 3 parts apple cider vinegar and 1 part salt. Do this in a plastic or glass container. Do not use a metal container or allow your items to touch. Allow it to soak for an hour.
Preheat your oven to 450° F. Set your item on a cookie sheet covered in aluminum foil (the foil is to protect your cookie sheet). Bake your item anywhere from 15 minutes to an hour, checking periodically for color change.
Repeat the process for more aging. Your subsequent soaks and baking times can shorten to a 5-minute soak and 15-30 minute bake.
Ammonia and Salt
Seal your item in an air-tight container with ammonia and salt, and allow the vapors to do the trick. You don’t want the ammonia to touch the item, so suspend the item above the ammonia, place a separate container of ammonia inside, or soak paper towels in the ammonia and wrap your item inside. Check it every few hours or days. Replace the ammonia daily.
Cut boiled eggs into halves or quarters and put them in an air tight container or bag along with the item. Do not let the eggs touch the item.
Liver of Sulfur
This is a gel that you add to hot water. You can soak your items in the bath for a few minutes to get a darker color.
Dilute some bleach in water and soak your item for a few minutes.
Birchwood Casey Aluminum Black
But some blackener and apply it lightly to your item. This product can turn your item completely black.
Soaking your steel in vinegar overnight can darken it. If you just want to irregularly stain steel without as much of a rust effect, try applying a paper towel or sawdust soaked in apple cider or balsamic vinegar, or other acids like lemon juice, grapefruit juice. Also try directly applying mustard.
Stainless steel is made to be resistant to oxidation, so the usual methods don’t work as well. Try ferric chloride, also sold as circuit board etchant, or sodium bisulfite.