Rheoscopic fluid

Rheoscopic fluid literally means "current showing" fluid. Such liquids are effective in visualizing dynamic currents in fluids, such as convection and laminar flow. They are suspensions of microscopic crystalline platelets such as mica and glycol stearate. When the suspended particles are put into motion, they orient themselves in localized, preferential alignment, larger parts of the fluid moving sheer parallel to other parts of the fluid. With appropriate illumination, the particle-filled fluid will reflect differing intensities of light, making the movement of the currents visible.

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