Many players recommend using Spark of Legend on an epic item.
Spark of Legend requires a socket, but will grant the item an extra socket once it is placed.
Once a Spark of Legend is placed on an item, it is permanent. A Disenchanter's Sponge will not remove it, so be certain this is an enhancement that is desired prior to placement.
It is possible to recover the Spark of Legend by using an Artificer's Solvent. This will destroy the item, but will allow the user to recover the Spark of Legend for use on other items. This can be a viable choice even when dealing with epic equipment as you will often be able to purchase twenty of any epic item from the Emporium for every one Spark of Legend you find.
If you plan on giving old equipment that is enchanted with a Spark of Legend to a lower level party member, it will revert the equipment to the tier that is appropriate for the new character. If a player's goal is to give powerful items to low level party members, use of Spirit Guides is recommended over the use of Spark of Legends.
Spark of Legends can be obtained in Dimensional Pockets, which are obtained in survival mode (one for every 5 waves beaten), in the limits of evil campaign (one for each five floors completed, rewarded after the party leaves the dungeon) and for completing the Madness of Dreams campaign. However, even within the Dimensional Pockets, they are fairly rare and should be used sparingly. There are also VERY rare alters called Mystical Alters that can grant one Spark of Legend if they have the "A GIFT OF MAGIC" effect. These alters can be rarely found on any floor in a dungeon.
It is also possible to obtain Spark of Legends through premium content or by liking the game on Facebook through the game interface