Caustic Blood (3.5e Feat)
From D&D Wiki
Your magics allow you to make your blood highly corrosive.
Prerequisite: Boneshaper level 3, Shape bone class feature, 13 Con
Benefit: You may choose to have weapons you shape deal an additional 1d6 of acid damage. You may also choose to have armor you shape provide acid resistance 10. These effects cannot be applied to a weapon or armor that already adds elemental damage or resistance (except that provided by aweapon or armor crystal).
Normal: Weapons and armor cannot have elemental enchantments