Summarize:

Place your aluminum piece on a sheet of aluminum foil with the shiny side facing away from the aluminum piece. Fold the foil over so it covers the aluminum piece but is not sealed. The aluminum foil creates distortions as well as a rainbow pattern on the aluminum due to the heat and chemical reaction. Keep the open ends of the aluminum foil facing upwards so that the water can run down into the package. Stack your pieces in the dish rack of the washer. Add powdered dishwashing detergent, like Cascade Complete or Finish Dishwasher Powder, to the dispenser. Then, add 1 teaspoon of trisodium phosphate (TSP) to the dispenser. TSP can be found at your local hardware or home improvement store. Age the aluminum by running the dishwasher on the pots and pans cycle. Turn on the drying cycle as well. After the cycle is complete, carefully remove the aluminum pieces from the dishwasher. Use caution, as they may be hot. Remove the foil around the aluminum. If you want to add more patina or increase the aged look of the aluminum, wrap the pieces in aluminum foil at a different orientation and run them through the dishwashing cycle again.
Wrap your aluminum piece in aluminum foil. Load your aluminum pieces in the dishwasher. Fill the dispenser with powdered dishwashing detergent and TSP. Run the pots and pans cycle. Remove the pieces from the dishwasher. Repeat the process to add more patina.