Tempering your Armor and Weapons will increase the Physical Defense, Magic Defense, or Damage that the item provides.
In order to Temper an item, you will need a Tempering Stone, and equipment to Temper. Tempering Stones can be found from defeated bosses, or extracted from equipment.
Activate the Tempering Stone by right-clicking, and then select the item you wish to Temper. The Tempering Items window will display showing a relative Success rate, as well as the current and potential bonuses.
At higher Tempering levels, it is possible for an item to lose some of its bonus should the enhancement not succeed. You can choose to enable De-rank Protection for your attempt at an Ellun cost prior to confirming the Tempering.
If successful, your Armor and Weapons will display their increased Tempering bonuses in blue text. Additionally, each item will have its own maximum tempering which is displayed on the item itself.