You will find a lot of different methods - the best one is going to depend on your vision of "Antique Finish". Most are over done and few are done to actually reflect 20 years of hard use. One method will leave it looking like it has been left in a leaky barn for 100 years and another will make it look like a fake finish.
Now when I was a youngster, my Grandfather hated the new hat look. When he was forced to buy a new hat, he took into the back of the hat store and got it wet, he then walked out side and stood at the curb. In a few minutes a log truck came down the street and Grandpa threw the hat under the back wheels. Instant antique look. Made Grandpa happy.
If you look old and weathered and you want a gun that looks like you bought it 20 years ago and it has been your life long friend, then do not overlook your leather, clothes, boots and hat. When wearing new clothes with nice new leather a antique gun just plain looks out of place.
The above are only my views and yours may and will vary.