Aluminum is ideal for rings and bracelets. It won't turn your skin green, it won't oxidize or tarnish. It's lightweight but quite sturdy.
Because it doesn't oxidize, the letters are darkened with an oil-based ink. If the ink begins to fade over time, you can re-darken the lettering with a sharpie, and polish off the excess with a polish pad.
We are slowly dropping the aluminum option from many of our products because it's not much more expensive to make them in sterling silver.