Rheoscopic Fluid

With Rheoscopic Fluid, one is able to see minute flow patterns in a liquid. The effect of stirring, heating, and cooling small portions of the liquid in the container results in beautiful flow patterns.

Activity #1
Pour Rheoscopic Fluid into a clear, colorless container such as a beaker.

How does stirring affect the flow pattern? Stirring in a figure eight pattern is considered by some to be the most efficient method for stirring. Do you think this is true?
Hold a piece of ice near the edge of the container with a small portion of it below the surface of the liquid. What do you observe?
Place a small warm object such as a glass stirring rod or a metal spoon below the surface of the liquid and near the side of the container. What do you observe? Can you tell when the object becomes the same temperature as the liquid.
What happens when you place drops of hot water into the container near the side?
What happens when you place drops of cold water into the container near the side?
What happens when you place drops of the solution into the container from various heights? Note: In this case the drops and the solution will be at the same temperature.

Activity #2
Pour Rheoscopic Fluid into a flat tray with low sides. The advantage of using a clear, colorless tray is that different sheets of colored paper can be placed under it.

Set a drinking glass into the solution, resting on the bottom of the tray. Drag a flat spatula through the liquid and notice the flow patterns around the drinking glass.
Set other objects into the solution and notice the flow patterns around them. How do the flow patterns differ around objects with sharp right-angled edges vs. more rounded edges? Around objects slightly below the surface of the liquid?
Use clay to produce barrier outcroppings along the edge of the tray. How does this affect the flow patterns?
Try blowing through a straw to investigate the effect of air currents.

Explanation
Rheoscopic Fluid consists of a suspension of flat particles which are slightly denser than water. When at rest, the particles will settle to the bottom. Shaking or stirring brings them back into suspension. Small groups of flat particles position themselves in the stream of flowing liquid the same way. As these groups twist and turn, sometimes the flat sides of the particles face us and reflect more light; sometimes the edges of the particles face us and reflect less light. This explains why we easily see the swirling patterns

Note: Food coloring is often used to more easily see the swirling patterns.