Unstable Greater Hexweave Essence

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

Source
The original version of this item, Greater Hexweave Essence, was crafted by tailors with a skill level of 1. The recipe was learned from Recipe: Greater Hexweave Essence, which could be purchased from the Tailoring Emporium at Lunarfall or Frostwall, or from the tailoring vendor in Stormshield or Warspear.