well heres the problem black anodizing has a horrible rep for fading staining ect ect,
the sheen all depends on the surface finish prior and how long is was left in the sulfuric acid AND the grade of aluminum as well.
There is a lot of variables when it comes to getting parts anodized. I can help you out in this if needed I work at an aerospace/ag/plating facility let me know if you have any questions and i can ask the experts.
ALSO make sure, DAMN SURE there is no steel or stainless in the parts or you wont have any parts left, and some angry platers.
In my honest opinion if you want durability, go powder coat.
This is a small piece for my intake that I did at work, just hit it with a red scotchbrite pad then onto the process. dont mind my DIY distributor hold down (bead blasted and electroless nickle plated)
Matt