Soul Crystal engraving is a feature unlocked when the player reaches level 35. Soul crystals are used to raise the level of the soul engraving, which increases the effects of socketed gems. Soul crystals are found as drops only in multiplayer dungeons in the Hall of Heroes, and can be found normally in Mystery Chests. As the level of the soul engraving increases, the amount of soul crystals required to level increases.
In the soul engraving interface, the player is shown the experience bar of the engraving, as well as the level of the engraving. Also listed are "current level" effect and "next level" effect. If a player has soul crystals, then the amount possessed will show and the player will be given the option to engrave the crystals. Note that the player is given the option to manually type the number of crystals to engrave, meaning that if a player wished, they could engrave only some of the crystals they possess.
When the player reaches level 35, they are given a quest to increase the level of their soul engraving from level 1 to level 2. This requires 10 soul crystals. Upon completion of this quest, the player will be rewarded 100 soul crystals, which if engraved all at once, will increase the player's soul engraving level to 5.