Larian Studios Forums Divinity - Original Sin Divinity Original Sin - Help/Tips/Tricks Tenebrium weapons?

The Smith in Sacred Stone has plenty of Tenebrium weapons.
Alternatively just use a Tenebrium Bar on any weapon other than a staff. (If you want to use it for the quest, it better be something without elemental damage.)

You will only need Tenebrium weapons once to kill an object that is immune to the other damage types.
That being said you will be able to deal more damage with Tenebrium enchanted weapons than regular weapons, because your Tenebrium skill can be brought to a higher level than your weapon skills.