Summer STEM Challenge – Fireworks in a Jar

Nothing is actually exploding or burning in this jar — the "firework" look comes down to three simple science concepts: density, solubility, and diffusion.

First is density. Oil is less dense than water, so no matter how you pour it, it will always rise and sit in its own layer on top — the two liquids simply won't mix together.

Second is solubility. Food coloring is water-based, not oil-based. That's why the drops sit as tiny separate beads inside the oil instead of blending in — the coloring is waiting to find water, its natural match.

Third is diffusion. The moment a droplet of food coloring breaks through and touches the water, it spreads outward in every direction at once. That spreading motion is what creates the colorful, explosive-looking bursts.

This same set of processes shows up everywhere: it's why dye disperses in a glass of water, how sugar dissolves into coffee, why ink bleeds outward on a paper towel, and even how nutrients move through cells in your body. Fireworks in a jar aren't magic — they're a small, safe demonstration of chemistry happening all around us, all the time.