To age brass, you can just use some brass darkening solution or liver of sulfur, which is pretty ho-hum, but gets the job done.
Or you can have some fun and get it done too, by smoking the part in black powder smoke.
To do small parts, you’ll need a;
5 gallon bucket.
A wire to suspend the parts inside the bucket.
Some clear cling wrap to cover the top of the bucket. Have this unrolled and ready cause you need to cover the bucket quickly.
A long stick with a match taped to the end. Those long wooden barbecue matches work well if you tape two or three of them together.
A Big Devilish Grin, and some black powder.
So, with parts on hand, locate your bucket in a convenient location,,, although this should not be inside the house as the smoke stinks up the furniture something terrible.
Cut a piece of wire and bend the ends so it sits across the center of the bucket, then bend some short pieces for hangers, and hang your brass parts down into the bucket.
Next, put your charge of black powder in a pile in the center of the bottom of the bucket. . I use 4F, and 15 or 20 grains works well,,, a half ounce makes way too much smoke!
Now you’re about ready, so lock up the dog and get the kids back out of the way.
Being sure you have your cling wrap close at hand, light the match and gingerly lower it into the bucket toward the pile of powder. Full face mask, safety glasses and gloves are recommended, but gritting your teeth, turning your head and closing your eyes are an option.
Poke the flame into the powder.
You will more or less immediately hear a big Whhooosh!
In a smooth fluid motion, quickly pull out the match and grab the cling wrap and cover the top of the bucket! You want to trap all the smoke possible.
Depending on the brass, 5 or 10 minutes will turn it a mustard color, 10 to 15 minutes a brownish yellow, and longer will eventually turn it black.
When the parts get to the color you want, take them out and rinse them in water, then dry them. Rubbing them with a cloth will highlight the edges.
John