A large glass jar with a blue jade lid, typically found heavily sealed with wax. The contents of the jar is pure whiteness and it glows faintly in deep darkness.
This jar contains solid cloud which can be pulled out completely or in part to up to roughly 200’x200’x10’ of volume. The cloud will not form thinner than 10’ in any dimension. Should multiple jars be found the material can be combined. The cloud will not enclose solid objects when forming nor will it form anywhere save under the open sky.
The cloud is very buoyant and can support stone structures as tall as the cloud is thick. For purposes of taking damage, the cloud is as durable as hard stone and is unaffected by fire. Normal winds have no effect on the cloud. Powerful storms can affect objects and beings on the cloud, but not the cloud itself.
The being who removes the cloud from the jar is able to control the cloud mentally, which can move up to 10 mph with trivial loads (i.e adventuring party with horses,etc) and up to 3 miles per hour when permanent structures are built atop it. The clouds have a ceiling of 1 mile and can rise and descend at the same rate.
If the jars are lost or destroyed the cloud becomes free travelling and moves with the winds.
Legend has it that this cloud is obtained by harvesting it from a particularly rare cloud formation on the Elemental plane of Air, and that location is especially hazardous due to a preponderance of dragons.