Making Clear Ice by Releasing Trapped Air

Finally, I've got a minor success in my clear ice experiment to share. So far in an attempt to make perfectly clear ice in my home freezer, I've tried:

• Distilled vs. Tap Water
• Melting and refreezing water
• Hot Water vs. Cold Water
• Carbonated Water vs. Still Water
• Horizontal vs. Vertical Container Shapes

Noting that water freezes into ice from the outside-in, leaving an air/water bubble that forms the cloudy part of ice, I sought to devise a way to either change the way ice freezes, or to release the trapped air while the ice was freezing.

First I tried laying a bar spoon diagonally through the water. The theory was that the metal of the spoon might conduct coldness into the center of the ice so that the ice would freeze more evenly. The intended result was a dispersed air throughout the ice rather than just in the bottom/center layer. 

But alas, the intended result did not happen. There does appear to be more air dispersed in the ice, but still the majority of it is in a layer along the bottom.

Next I tried inserting a straw into the center of a tray of ice to see if the air would escape through the straw. The plan was flawed to begin with, as water would probably just freeze inside the straw so no air could get out.

In reality the freezing ice pushed the straw up so that it was only inserted about half an inch into the ice by the time it was fully frozen. This had no effect on the amount of cloudiness.

For something that did work, keep reading after the jump.

In one experiment, I was waiting for ice to freeze (this is what I do with my spare time) and noticed that the ice had frozen all around the outside perfectly clearly, leaving the center full of yet-unfrozen water (and our old enemy-trapped air). So I poked a hole in the top with an ice pick and released all the water.

Then I refroze the ice to make sure it would stay clear. It did.

And I produced my first batch of perfectly clear ice. Hooray!

Now that's a sexy bowl of ice.

Conclusions: To release the air bubble in the center of ice, a straw does not work. Neither does attempting to disperse the air by using a spoon or other conducting material. But if freezing ice is stopped before completion and the unfrozen center drained, one is left with a very clear, but hollow, block of ice.

Future Experiments: Most people will not have the time to wait around until a block of ice is just frozen enough to poke a hole into. Thus it would beneficial to devise a system that releases the trapped water/air in the center of a freezing block of ice.