Aluminum has a matte grey finish. There is a subtle sparkle caused by the silicon particles in this material. Because this material is printed with support structures that are removed during post processing, certain surfaces (where the structures were) can be slightly rougher, while the others are more smooth. The supports are required in order to avoid sagging into the loose powder below that can cause warping or imperfections in your model. Sometimes, these supports are difficult to remove and leave behind an imperfect surface. The production planners do their best to orient your models optimally to minimize the amount of support structures needed.
Aluminum is the only metal we offer that is fused and melted using a laser from a bed of metallic powder. The 3D printing process is called selective laser melting. Fabrication takes place on a build platform with supports to anchor the part. A bed of aluminum powder sits above a build platform. One layer at a time, the powder is melted by a high powered laser. The melted powder is quickly cooled to solidify the metal. To form the next layer, the build platform is lowered and a new layer of powder is distributed with a coater. This process is repeated layer by layer until the part is complete. Horizontal areas and edges print with an automatically generated support structure to prevent the feature from sagging into loose powder. The support is then removed and polished away from the part during post-processing.Selective laser melting is unique because the high power laser provides enough energy to heat the aluminum powder above the melting point. This process fully melts the powder rather than just sintering it, creating a solid, homogenous aluminum alloy.