The list has been updated to match the changes done in version of the game.

Originally Posted by ivra
It seems the necessary tenebrium skill increases as the item level of the weapon increase. For instance I managed to add tenebrium damage to an item level 1 weapon with only 1 in tenebrium. For a item level 19 weapon I needed tenebrium 4 (I actually do not know if tenebrium 3 is good enough, but I know that tenebrium 2 is too low). Need to test a bit more.

The requirement is Tenebrium 3. The reason I managed to upgrade a level 1 item with only 1 in the Tenebrium skill is that I happened to use a level 1 'Fighting Knife'. All other level 1 items I have tried to enchant with tenebrium requires a Tenebrium skill of 3. I guess the level 1 'Fighting Knife' is a little bugged.