Received from: Bulletin board in the Mages Guild [Hatmandor Region] (M12:7)
You will receive this mission after completing one quest from the bulletin and afterwards reading Polite request.
The mission consists of gathering four pieces of beaver fat [Desert] (M20:38) - the beavers shouldn't cause you any problems. It's best to shoot them from a bow.
Once you collect enough, return (teleporting would be best) to the Mages Guild [Hatmandor Region] (M12:7), where you will find a room with an alchemic stove (on the same floor that the Bulletin board). Throw the fat inside and pull the lever beside. After it melts, take out the black candles.
Accordingly to the request in the letter, take the candles to the field hospital (M12:3) and leave them in the basket, found behind the screen.
After completing the mission, return to the Mages Guild (M12:7) and collect you prize from the chest.