On the inside of the form i sand blasted it which on aluminum creates a gray matte effect. On the outside i wire brushed and polished giving it a glassy mirror like quality. You can also patina aluminum though its unnecessary if the desire is to avoid rusting since aluminum wont rust (its nonferrous). Do note that patinas that are meant for coloring bronze a certain color will act differently on aluminum, iron, and any other metal you choose to cast.