Magister Ladd:
Ah, you are back with the pure silver and true gold! Good! You are almost ready to get Mimir's Elixit, but listen carefully! In order to create the elixir, you need to melt the two ingredients fast and perfectly. Normal fires are not hot enough to achieve that. Only Blood fire is hot enough to meld true gold and pure silver.
You can obtain Blood Fire by killing the bloody guardian in the Lair of Antharas. Don't worry, the Blood Fire is inactive when you simply carry it with you. It will not burn you... So go now and gather this last piece. Then come to me and I shall instruct you how to create Mimir's Elixir.