The skill of creating material objects from astray is called astralcraft.
The possible creations of astralcraft are limited
only by imagination. Physical properties such
as color, hardness, size, and complexity are all
dependent on the crafter’s ability to manifest these
properties in their mind’s eye. Raw intelligence
also governs a creation’s function, as well as how
long it lasts before drifting back into the vaporous
astra which surrounds it.
Anyone in the Astral Sea can conjure an amor-
phous bubble of mass, but geniuses of astralcraft
can paint cathedrals in thin air, visualizing every
brick and plank. These creations last for weeks,
and the master astralcrafters among bat-kind can
render an object from astral permanently.
Astra cannot exist in other worlds. When a
conjured object leaves the Astral Sea, it vanishes
instantly.
TODO: Rules and such...