Antiquing means creating a patina, a greenish film on brass, so it appears mildly corroded, or gently aged. Certain substances like bleach, vinegar, ammonia fumes and saltwater produce different types of patinas on your brass. To successfully antique brass, start by cleaning brass using mild soap and water to remove all grease. Remove varnish using nail polish remover containing acetone or use a paint stripper.
Ammonia Fumes Method
Cut a piece of plywood so it fits at the bottom of the plastic container like a shelf, a few inches up from the bottom.
Pour 1 cup of ammonia full-strength into the bottom of the plastic container. Put your brass item on top of the plywood, then place the cover on the container. You will notice the brass begin to darken in a few minutes or hours, depending on the humidity and temperature. The brass will start to turn a dark green color.
Cover the container again if you want to continue the tarnishing process.
Remount or reattach the brass item to the furniture or appliance, then wax and polish the tarnished brass to convincingly make it appear antique or leave the finish unpolished and tarnished.
Acid Drip Method
Put on rubber household gloves. Make certain you have good ventilation in the room.
Mix a solution of 10 parts water at room temperature to one part antiquing solution in a plastic or ceramic bowl large enough for your brass item.
Place your brass item in the solution and move the item around. This gets rid of air bubbles which can create spots during the tarnishing process. The brass item will begin to darken right away, from pink to a red-brown to brown-black in color.
Remove the brass item from the bowl when you see your desired color.
Rinse the brass item well under hot water. Using a sponge, wipe the item to clean off the powdery residue. If the brass appears too light, place it back into the bowl of solution. If the brass looks too dark, scrub it with a scotch pad to restore the metal, then start over by placing it in the solution.
Dry the brass item completely using a soft towel, if you feel happy with the color and outcome. Leave the brass as is and it will continue to age or you can preserve the finish by using a lacquer or beeswax.