Steampunk fashion and art is full of brass, copper, and iron. All fantastic and beautiful metals, but there is an often overlooked material that is attractive, period appropriate and has an interesting history.
Aluminum is a readily occurring element on earth, though it is mostly found in the form of oxides and silicates. It was not named until 1807 and was not isolated as a pure metal until 1825 by Hans Christian Ørsted. The early processes were very inefficient, slowly producing very small amount of impure metal.
This made Aluminum more expensive than gold, sliver or platinum. Napoleon III had given banquets where the most honoured guests were given aluminum utensils, while the other guests had to make do with gold. When the Washington Monument was completed in 1884 it was topped with an 100 ounce aluminum capstone in an elaborate dedication ceremony.
Electrolytic and chemical extraction improvements in the 1880's lead to mass production of the metal, making it the accessible and affordable material it is today.
So depending on your particular steampunk ethic and adherence to "the-past-that-was", consider the inclusion of Aluminum in your props and costumes.
Note: Both "Aluminum" and "Aluminium" are acceptable spellings. How fun is that?