A brass item is considered antique if it has attained the age of 100 years or more. However, like the term "burnish," the term "antique" also refers to a finishing process that creates the semblance of age.
"Burnishing" and "antiquing" are synonyms for the same process. The terms are used interchangeably. The term burnish means "to polish" or refers to the shine of an item. This seems contradictory to a process that patinates, creates a patina, rather than creates luster. In this context, burnish refers to its etymological origin. The Anglo-French transitive "burnir" means "to make brown." The terms "antiquing" dates to 1920s America.
Antiquing or burnishing can only be achieved with unlacquered brass. Protective lacquer stymies the chemical reaction that creates the false patina. Brass plate alloyed with steel or zinc can be antiqued, but color will be unpredictable.
One method uses commercial antiquing fluid. Mix one part antiquing fluid to 10 parts water in a nonmetal bowl and apply.
Another effective chemical is ammonia, which creates a verdigris finish.
One cup vinegar to one or two tablespoons of table salt creates a nontoxic solution. Allow brass to sit overnight and by morning a brown or slightly green patina will appear.