Prefer stainless steel hardware, but bolt heads need to be black for this project, which involves decking with protruding dome-shaped bolt heads. So cargo will be sliding back and forth on top of the heads. Is there a reliable, durable, scratch-resistant way to turn the bolt heads black--or find identical bolts that are black to begin with? Is black oxide the only choice? (My impression is it's not particularly durable.) Thanks for any help!