Ash

Ash is the remnants of destroyed undead. First discovered in the Dark Caribbean. Known to have physiological & psychedelic effects when consumed. Extremely valuable. Responsible for numerous conflicts, trade disputes, and an influx of black markets. Addicts can be spotted by their sunken eye sockets, darkened lips, and faintly glowing bones.
There are markets for this Ash in Many Ports throughout the Dark Caribbean. Most often Ash dens (Much like Opium Dens or Drug Houses) these locations serve as Trade and distribution centers and places to partake and succomb to the affects of the Ash.
Since Ash Comes from the Bones of Skeletons there often is incentives for Pirates to Hunt Skeleton Crews as the Ash can often fetch better prices sometimes than stolen cargo. Not every Skeleton destroyed turns into Ash it only occurs when the bond between thier Commander or Master is broken as to produce an Arcane rift between the two that their bones explode into ash rather than tumble to the ground.