Kinetic sand drawing.

Basically you have a ball rolling through sand creating patterns.

You can see some example images and videos with a [Google search](https://www.google.com/search?q=kinetic+sand+drawing+table&newwindow=1&safe=active).

It looks like it works best with fixed patterns, rather than random rolling, but you could start with a simple spiral. Enhancements can include multiple balls or the ball affecting the colour of the sand.