Why does some ice come out white and cloudy, and some come out clear?
Look… two ice cubes from the very same water. One came out white and cloudy, and one came out clear as glass! Here is a little secret: water is hiding tiny bubbles of air inside. Now we will freeze this cup, with the cold sneaking in slowly… from the top. Ready to guess? Will the ice be white… or clear?
After you watchWhy does some ice come out white and cloudy, and some come out clear?
The short answer
Ice looks white when tiny bubbles of air get trapped inside it, and clear when the air gets swept out. Water is hiding invisible air. If the cold freezes a cube on every side at once, the air gets trapped in a white cloud in the middle. If the cold freezes slowly from the top down, it pushes the air down and out, so the ice comes out clear.
Try this next
- What if you freeze the same water but only let the bottom get cold? Guess first: which way will the white cloud move this time — up or down?
- What if you stir the water hard first to shake some air loose? Guess before you freeze: will shaking some air out make the ice a little clearer?
The whole story
How it works
Tap water has air hidden inside it that you can't see. Ice can only hold pure water, so as the water freezes, the cold edge shoves the air ahead of it. In a freezer the cold grabs every side at once and the air gets squeezed into the middle and sealed there as a tiny white cloud. When the cold comes slowly from just the top, one freezing edge keeps pushing the air down and down until it leaves out the bottom — and the ice comes out clear.
What people get wrong
Lots of kids think white ice is dirty. It isn't! The white is millions of tiny air bubbles, not dirt. The same clean water makes clear ice if you freeze it slowly from one side.
The catch
Freezing fast on every side is quick and easy — that's what every freezer does — but it traps the air, so the ice is white. Freezing slowly from the top makes pretty clear ice, but it's slow and you have to be patient.
Questions kids ask
Is white ice dirty?
No! The white is lots of tiny air bubbles that got trapped when the ice froze, not dirt. The same clean water can make clear ice if it freezes slowly from one side.
How do you make clear ice at home?
Let the water freeze slowly from the top down, like in a little cooler with the lid off. One freezing edge keeps pushing the air down and out, so no bubbles get trapped and the ice comes out clear.
Why is my freezer ice always white in the middle?
Because the freezer cold grabs every side of the cube at once. The air gets squeezed into the middle and sealed there as a tiny white cloud.
Talk about it
- Hold up a cube from the freezer — where do you think the white part is hiding before we look?
- If the white is trapped air and not dirt, how could we make clear ice from this same water?
- Where else have you seen air sneak into water with nobody pouring it in?
For grown-ups
Water holds dissolved gases (mostly nitrogen and oxygen), and gas dissolves more in cold water. A growing ice crystal rejects that dissolved gas at the freezing edge. When a cube nucleates on all faces and freezes inward, the rejected gas is sealed as microbubbles at the last-to-freeze core — the cloudy center. Directional freezing keeps a single advancing front that pushes the gas into the remaining liquid, which is why clear-ice makers freeze slowly top-down and discard the gas-rich bottom.
Keep going
What else makes you wonder?
- What if the cold came in from the bottom instead of the top — where would the air go?
- Where else is air hiding that you can't see until something changes?
- What other things turn white when tiny bubbles get trapped inside them?