I've used acid. salt water electrolysis, Casey's blue, media blasting from soda, walnut shell, sand bead etc. Sometimes a combination of these. Wire brushing works for an uneven finish that looks aged on aluminum and other treatments added after brushing can be interesting.. Casey's makes an aluminum black that can be buffed for varying effects.
Keep in mind aluminum starts oxidizing immediately after brushing, sanding, blasting, polishing etc. I've found that using vinegar on the part, soaking for a day or less will really jump start the process. Rinse the part in soda water bath to stop acidic action when the part suits you.
Using acid is dangerous so learn things before you try it. Don't use acid in a shop area. The fumes will rust every metal thing in the shop. Work outside and use a respirator, gloves and full face shield....better yet don't use acid. It's fast if you know what you're doing, but can ruin your life in a moment if incorrectly handled.
The previous suggestions made are good too. Metal patina is an art form in and of itself especially in architectural design and ranges from wrought iron to brass. There are a lot of paint on products that can even be applied to plastic, card board , wood etc. that can fool most anyone into thinking it's brass or wrought iron etc. Oil and heat on iron and steel can produce fantastic finishes that will seal against excessive corrosive effects over hundreds of years and look beautiful from day one on, actually age only makes them more interesting with changing patina patterns.