Rainbow in a Glass

Create beautiful color layers and learn about density!

About the experiment:

Have you ever wondered why some liquids mix while others don't? This rainbow-in-a-glass experiment is a visually stunning way to explore the concept of density. By carefully layering different liquids, you can create a mini rainbow in a glass!

Required materials:

Tall, clear glass or jar
Honey or thick syrup (e.g., corn syrup)
Liquid dish soap (preferably colored, e.g., blue or green)
Water (can be colored with food coloring, e.g., red)
Vegetable oil
Rubbing alcohol (can be colored with another food coloring, e.g., yellow or purple)
Spoon or dropper for careful pouring

Step-by-step instructions:

Start with the densest liquid: carefully pour a layer of honey or syrup to the bottom of the glass.
Next, very slowly pour the dish soap over the back of a spoon so it flows down the glass wall. The goal is for it not to mix with the honey.
In the same way, add a layer of (colored) water.
Then carefully add a layer of vegetable oil.
Finally, very gently add a layer of (colored) rubbing alcohol.
Observe your rainbow! Each liquid should form a separate layer.

The science behind it:

Each liquid has a different density. Density is a measure of how 'heavy' a substance is for its volume. Denser liquids sink below less dense liquids. In this experiment, honey is the densest and therefore stays at the bottom, while rubbing alcohol is the least dense and floats on top. The other liquids layer in between according to their relative density.

Tips for success:

Pour very slowly and along the glass wall to prevent mixing of layers.
Using food coloring helps make the layers more visible.
If the layers mix a little, wait a few minutes; they might separate again.