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Choose a container large enough for your aluminum pieces to fit inside and be completely submerged. Sprinkle a few tablespoons of an oxygen-based cleaner (like Oxi-Clean, Clorox Oxygen Action, All Oxi-Active, or Shout Oxy Powder) in the bottom of the container.  You can make your own oxygen cleaner by combining 1 part sodium percarbonate (dry, powdered hydrogen peroxide) and 1 part sodium carbonate (washing soda or soda ash).  Take care not to confuse either of those powders with sodium bicarbonate (baking soda). If you’d like your aluminum to have patterns in the aging, you can create them with aluminum foil. Crumple up several pieces of aluminum foil and place them in the bottom of the container, on top of the oxygen-based cleaner. Press them flat into the bottom of the container. Add a few more tablespoons of oxygen-based cleaner on top of the aluminum foil. You can put templates, gears, or other items on top of the aluminum that will prevent the covered sections from being aged, if you’d like to make designs or shapes on your aluminum. Several tablespoons should suffice. Spread the cleaner evenly over the metal and try to avoid building up piles of the powder on top of the aluminum. In order to keep your aluminum pieces from floating in the water, place a heavy object on top of them. You can use another piece of metal like a weight or a gear, or even a wrapped stack of dinner plates. Pour cold water in the container until the entire piece of aluminum is submerged. Add up to ½ inch (1.3 cm) of water over the top of the aluminum to ensure it is completely covered. Carefully tip your container a little bit to one side and then the other in order to get the oxygen-based cleaner to flow. If the container is too heavy for you to move, gently agitate the mixture with a long spoon. Swirl the mixture to get the powder to flow through the water. The oxygen bubbles produced by the cleaner are what cause the oxidation of the aluminum and make it change colors. Though you may begin to notice the aluminum changing color after four hours, for best results you should leave the aluminum to soak for at least 24 hours. You can leave it for up to two days if you desire a deeper color change. Take the aluminum piece out of the water. Use a razor blade or the edge of a plastic card (like a hotel room key or credit card) to remove any heavy crusts of oxygen-based cleaner left on the aluminum. Mix 1 tablespoon (14.8 ml) of distilled white vinegar with each cup of water. Pour the mixture over the aluminum or soak the aluminum in the mixture for a few minutes. Then rinse the aluminum with plain water. Set the aluminum in a dish drainer to dry, if the piece is small enough, or prop it against a hard surface to dry if the piece is large. This aging process creates flowing gray tones in the aluminum.
Sprinkle oxygen-based cleaner in the bottom of a container. Place crumpled aluminum foil in the container to create patterns. Lay your aluminum pieces on top of the aluminum foil. Sprinkle more oxygen-based cleaner on top of the aluminum pieces. Place something heavy on top of the aluminum. Pour cold water in the container. Tip the container gently to get the cleaner to flow. Add another few tablespoons of oxygen-based cleaner to the water. Allow the aluminum to soak for at least 24 hours. Remove the aluminum from the water. Rinse the aluminum with water and vinegar. Allow the aluminum to dry.