Big Reaction: A waterfall of light with Fluorescein

This riotous stream of oozy green color is produced by dropping Fluorescein dyes into water or alcohol. It’s an organic compound, the same stuff you find in highlighter markers. In its pure form, it has a rusty red color, which you can see a bit of in the gif above.

Fluorescein (C₂₀H₁₂O₅) emits light with a peak at 521 nm. Under a black (UV) light, as in this example, it fluoresces beautifully.

The full video is below. It’s short, and absolutely worth a look.

Bonus video! Here’s Fluorescein being used to show how sponges pass water through their body cavity.