How to protect the patina of your antique brass:
Once the brass piece has been antiqued using any of the techniques, the surface can be left unprotected. It will continue to naturally age and oxidize with the exposure to air and the elements. It will achieve a darker, richer tone. Oils from finger prints will also darken the piece as it is handled.
It you want to preserve the antique patina, it needs to be protected from the elements. A temporary, less permanent method is to use some type of wax. It can be beeswax, furniture wax or car paste wax. Commercial paste waxes specially made for metal preservation and protection are available such as Renaissance Wax or Johnson Wax. The piece can be warmed in the oven or with a hair dryer to make the wax easier to spread. Use a clean, soft lint free cloth to thoroughly rub the piece. Be sure to cover cracks and crevices. Remove excess wax and let the piece dry.
As another option, the piece may be covered with a lacquer. Use a clean brush or cotton balls / swabs and coat the piece evenly. Apply in thin layers. Lacquer spray is available and can be used on small pieces. Allow the piece to thoroughly dry before handling the piece.
Pieces exposed to the elements will need more regular care and restoration of protection than objects kept covered or inside.