War Mage Artius:
You collected them all. Well done! Now listen carefully.
Now we must purify this substance. To do so, we will need help from the Mother Tree. You must approach with care -- the residents of the Elven Village may well attack you rather than allow you to bring so dark a power near their sacred tree.
Still, you must go to the Mother Tree north of the village and purify this Powder of Broken Darkness into Powder of Broken Light. Then bring it to me at once.