Krieg the Psycho's 'Salt the Wound' skill in the Mania skill tree is described as:
When Krieg takes damage while his shield is down, it adds a stack of Salt the Wound to a maximum of 20. Krieg's melee damage and shotgun damage increase for every stack accumulated.
How exactly will Krieg get a stack added with Salt the Wound? Is it based on the amount of damage dealt to him? Or how long he's being damaged? What corresponds to one stack added?
How do I make getting Salt the Wound stacks faster?
I also would like to know if items like the Skin of the Ancients relic, which increase resistance to damage from various elements and including non-elemental damage, could lessen the speed at which Krieg gets Salt the Wound stacks.