Speak with Kalraath L'Vin near the North Freeport gate ( -6, 0, 63 ) /waypoint -6, 0, 63.
You receive Alchemical Medium (NO-TRADE NO-VALUE) in your inventory. This must be returned to Aldera. Should you destroy it, or lose it for some reason, then you can speak to Kalraath L'Vin again to receive a new one.
Return to Aldera V'Exxa for your reward. Pay attention to the dialogue, she will do a little quiz with you before giving the next quest.