When aged, brass develops a beautiful, nuanced patina that lends a subtle softness to decorative applications. Because of the stark contrast between the marbled look of aged brass and the gleam of new brass, many builders and decorators use chemical agents to accelerate the ageing process and create a patina in a matter of hours or days. There are a number of different solutions that will age brass, each of which creates a unique colour and effect.
Clean the brass thoroughly. Use acetone and a soft-bristled brush, scrubbing gently to remove any impurities from the surface of the piece. Never use steel wool or a metal-bristled brush, as these materials can scratch the surface. Rinse away the acetone under running water and allow the piece to dry thoroughly.
Select an ageing solution. There are many chemicals that will age brass, each with its own unique attributes. A combination of vinegar and salt will create a traditional, chestnut-brown patina. A combination of nitric acid and copper sulphate will produce a much more pronounced, dark finish. Household bleach will remove some of the harshness and shine from the finish while keeping the brassy colour. Ammonia vapour will create an extremely dark finish.
Place your brass item inside of a lidded container that's large enough to allow space on all sides. Pour the ageing solution into the container until the brass is completely submerged. If you're using ammonia, simply saturate a cotton ball for small brass items, or a rag for large jobs, and place it in the container beside the brass.
Seal the container and allow the solution to sit for 3 or 4 minutes. Open the container and check the patina level of the brass. If you would like a darker finish, allow the brass to continue to sit covered, checking every 3 minutes until you achieve your desired effect.
Remove your item from the solution, and rinse it thoroughly under running water. Allow the brass to dry thoroughly before use.
Verify before you attempt to create an artificial patina that your item is 100% brass. Items that are only brass plated can be irreparably damaged by the ageing solution.
Always wear eye protection and gloves when handling caustic chemicals.