Unstable Powerful Truesteel Essence

Unstable Powerful Truesteel Essences are what remains of Powerful Truesteel Essences, which can no longer be crafted. Prior to Shadowlands, using this item "restored" it into a Truesteel Essence and 25 Sorcerous Air.

Source
The original version of this item, Powerful Truesteel Essence, was crafted by blacksmiths with a skill level of 1. The recipe was learned from Recipe: Powerful Truesteel Essence, which could be purchased from The Forge at Lunarfall or Frostwall, or from the blacksmithing vendor in Stormshield or Warspear.