Cursed Essence

Cursed essence is a magical agent often used in tanning. It is also something of a curiosity, one that a simple tanner can't readily explain. It goes further than simply binding itself to material; it latches onto it, almost parasitically. 

Demonologists have a theory that, although cursed essence drops from avernic demons of Dowdun Reach, it is actually cthonic in nature. It would explain the tendril-like tenacity.