Water cup, cooking oil, detergent, coloring, alcohol, stir bar, water.
Pour some detergent into the glass, drizzle a few drops of green food coloring, stir, and make a green detergent on the bottom of the cup.
Prepare a small half cup of red solution and slowly pour over the green detergent along the tamper.
Take a small half cup of yellow cooking oil and slowly pour it over the red solution along the glass.
Prepare a small half cup of blue alcohol solution, then slowly pour over the yellow cooking oil along the stir bar.
The four-color liquid did not mix together, a beautiful rainbow cup was made!
The greater the density, the greater the gravity of the object, so the dense liquid sinks, the small density liquid floats, the density of detergent > the density of water> the density of edible oil> alcohol density, so finally the cup is divided into four layers and becomes a rainbow cup.