Forming principle:
Due to the different density of the alumina and the sand,and the bubble buoyancy, when we reverse the glass cavity,alumina and sand will be sunk at different speeds to the bottom of the cavity.It can form unexpected different scenery just like grassland,desert,clouds,sunrise/sunset and so with distinct layers.How wonderful it is!

Operation:
Shake it gently to gather the sand at the bottom and separate the bubble.Then reverse the cavity.The sand will flow down slowly just like flying waterfall.

Common problem:
Sometimes the buoyancy of bubble is equal to the weight of sand,it may be stuck.It's normal phenomenon of small probability.