I filled hollow-walled acrylic cups with rheoscopic fluid (and a few drops food coloring), creating a swirling effect in the cup walls.
The cups are double-walled cups from Clear Acrylic. I drilled a ¼" hole in the bottom, then added Pearl Swirl concentrate and some food coloring, and filled the remainder with water.
When shaken, the fluid inside the cup walls does swirl. Although I tried to avoid bubbles, some remained; however they produce pleasantly turbulent trails through the liquid. I was hoping a hot or cold drink in the cup would produce visible convection, but I haven't been able to observe that.
The rheoscopic fluid is mica flakes (also used as a makeup supply) in water. The flakes settle out after 10 minutes to half an hour, and then can be recombined by shaking.
The pearl swirl and water mixture has a tendency to form lots of bubbles which take a long time to settle out. For the first cup I repeatedly added a few drops of concentrate and shook them up, to find the right mixture, but once I knew the right amount to add I didn't shake everything up until the ingredients were all in, and bubbles weren't such a problem.
To seal the holes I cut discs out of a plastic bottle. I tried both epoxy and super glue, and found it easier to get a good seal with epoxy. (Super glue, having low viscosity, did not form a good seal against the rough edge of the drilled hole.)
For coloring I added:
- red-orange: 3 drops yellow, 7 drops red
- pink: 2 drops red
- (blue: no notes)
- teal: 2 drops blue, 1 drop green
The cups were 8oz dry and 13oz with water in the walls. I used about 140 drops of Pearl Swirl concentrate; that is higher concentration than I used when experimenting in a large test tube, since the area in the cups' walls was very thin.
I tried adding mineral oil ("baby oil") hoping for an effect similar to liquid motion toys. However, the mineral oil tended to stick to the acrylic walls (especially in the narrower top parts) leaving behind large oil bubbles. And while adding a few drops of dish soap avoided sticking, it resulted in many small water bubbles in the oil which settled out very slowly.
I was inspired by various other displays using rheoscopic fluid:
- The Peabody Essex Museum had a rheoscopic coffee table
- Boston's Museum of Science has a slanted table with rheoscopic fluid flowing down it; visitors can introduce obstructions and see turbulent flow around them. It's similar to this flow tank, but near-horizontal and with an open top.