Prizzed pain ring and Barbs support question

Question:

Does thorns damage from Prizzed pain ring or Barbs support is "added damage" to skill which hit or it have independent modifiers?

Which crit chance/crit bonus will be used: from skill/weapon or from skill?
And will anothe supports from skill (i.e. brutality) affect this thorns damage?

Pretty sure it is still thorns damage, so it does scale with global phys/damage mods, but not with any attack/melee mods.
Thorns have their own crit chance, base is 0% I think theres a tree node to make them crit.
I guess that support gems for the skill dont effect them, since the thorns damage is not added to the skill, but not sure.