Model builders, creators of replica items and metal sculptors sometimes wish to make metal objects look aged. Aging metal involves speeding the natural process of air and water interacting with and degrading the surface of the metal. To achieve an aged look for aluminum objects, the finish on the aluminum must be darkened. While it may be possible to age other metals with household chemicals, a prepared commercial chemical must be used for aluminum darkening.
Clean the aluminum with a solvent that leaves no residue. Examples include lacquer thinner, acetone and alcohol. Solvents such as kerosene or mineral spirits leave residue and should not be used.
Abrade the aluminum surface if discoloration from oxidation is present. Use an abrasive pad or other method.
Apply an even, thin coat of chemical aluminum darkener onto the surface of the aluminum according to the manufacturer’s directions. Chemical treatments can be brushed on, applied with a swab or cloth. Larger surfaces can be sprayed using a spray bottle.
Observe the chemical reaction and reapply another coat of the chemical darkener over the first one when it appears that the chemical reaction has slowed. Continue this process until a uniform darkened finish has appeared on the aluminum.
Dip a natural sponge in warm water and squeeze out excess water. Sponge off the chemical darkener with the damp sponge. Frequently rinse the sponge in clean water.
Mix 2 tablespoons of baking soda in a gallon of warm water to rinse large or complex aluminum shapes. This will neutralize the chemical reaction.
Dry the aluminum with compressed air or a hair dryer set to warm.
Seal the aluminum with lacquer or wax to preserve the darkened finish.
Larger hobby stores may carry chemical darkener. You can also find it online at such places as Jax Chemicals (jaxchemicals.com) and Birchwood Casey (birchwoodcasey.com).
Remove all jewelry before using metal darkener.
Wear protective gloves and safety eyeglasses when using harsh chemicals.