https://fyfluiddynamics.com/2018/09/although-you-may-not-recognize-the-name-youve/

These things, I can't spell. A rheoscopic fluid is one in which you can see the flow. Usually achieved by particles of particular dimensions longer in one axis, when they line up with the flow they interact with light differently to create pearlescence.

Refining pigment from dirt is a bit beyond me. I don't even know how I'd approach that. There is ironstone I could smash up and make a black one from though... maybe interesting with pottery actually... but no I bought some mica.

I was going to make some of those goofy "potion" bottles and do the toy for little ones at the same time. Since all the same testing applies.