"Burning"

With slight simplification, current takes the path of least resistance, so the current density will be higher where the anodes are close to the part than where they are further away, as well as higher at corners & edges, where it concentrates, than in the middle of the part where the current get shared across a larger area.

When electroplating, high current density (HCD) areas will be prone to "burning", a condition where the current demands deposition too fast for the electrodeposited metal to form a proper crystal structure and/or the current density is so high that not enough ions of metal are available at the point of deposition, so a lot of the current is wasted splitting water into hydrogen and oxygen.

The deposited metal is then rough, frosty-looking, and not bright ... a condition platers call "burned".

When anodizing, the same problem can exist as in plating ... but burning can have an additional cause. Anodizing must always be started at a low voltage because bare aluminum has low electrical resistance; then, as the insulative anodizing layer builds up, the voltage must be increased to keep the current flowing. Poor contact can prevent current flow at the low starting voltage for anodizing, then the current can later break through when the voltage is higher. If the aluminum is still bare when contact is thus restored, the high voltage + low resistance means the current will be far too high and severe burning will result..