Libram of Tenacity

With some work you can turn in the Libram of Tenacity to Mathredis Firestar to receive a Lesser Arcanum of Tenacity, which will permanently add 125 armor to your own leg or head slot item. Applying the Arcanum will make the item soulbound. You must be Level 50 or above to apply the Arcanum.

Required Materials

 * 1x Libram of Tenacity
 * 1x Black Diamond
 * 4x Crystal Ward
 * 1x Eye of Kajal
 * 30 gold

Source
Drops off level 50 and above humanoids or undead.

Patch Notes
As of patch 3.1, Lesser Arcanum can ONLY be applied to your own head or leg item. Applying them causes the item to become soul bound (tested on Commander's Helm of Defense) "Enchanting this item will bind it to you". You can no longer apply them through a trade window (tested) "Can only be applied to your own items". They require Level 50.