Understanding Rack Marks on anodized profiles
Because anodizing involves running an electric current through the part to be anodized, parts must be gripped by conductive racks or wires. Where these racks or wires contact the part, there will be slight unanodized marks or “contact points” left on the surface of edges of the parts. There are standards mentions and specifically allows for these rack marks.
Rack marks can be controlled by specifying on a drawing allowable locations for gripping a part. If rack marks are critical, discuss possible racking options in advance with your anodizer.
In long piece silver anodizing of our solar mounting structure, we normally cut the two ends to avoid the contact mark without anodizing.