Trying to Make Clear Ice - page 2
Next I tried insulating the sides and the bottom of the container, forcing the ice to form from the top down. This would hopefully result in having the last bit of water being stuck at the bottom of the container. This is a 12-cup measuring cup. The gray insulation is more than an inch thick, and the bottom block of Styrofoam is two inches thick.
I used filtered water.
I left the water in the freezer overnight. In the morning, the ice was perfectly, perfectly clear! There wasn't a single bubble inside, below the ice.
No matter how I turned the container in the light, I couldn't tell if there was liquid water inside, or if it was solid ice. This looked extremely promising, but the only thing to do was to leave it in the freezer for a few more hours.
A few hours later, the victory was cancelled. A cloudy mass appeared as the center solidified, and the outer ring cracked as it expanded. Back to the drawing board.
My next plan was to heat the top of the freezing water with a flashlight.
I hoped this tiny white-hot bulb was enough to keep the top from freezing until the very end, leaving an exit route for the final, gas-rich liquid.
That didn't work. The ice didn't even seem to notice that the flashlight was pointing at it. It wasn't warm enough.
For anyone who didn't think a flashlight would work for 10 hours on one set of batteries, I confirm it will.
My next tactic was to get the flashlight bulb a little closer to the water.
I disassembled the flashlight and suspended it about a half-inch above the surface of the water.
In this photo, you can see how close the reflection was to the bulb.
The closer flashlight bulb didn't help.
In the morning there was a small reservoir of unfrozen ice around the bulb, but it wasn't large enough to prevent gas bubbles from being trapped in a donut-shaped ring around this warm center.
I had a thought that the container I was using was too optomistic. Maybe I should try making little clear ice cubes before I ventured into gigantic chunks.
My next attempt was to use a ziplock bag to flatten out my water test. I placed the flat bag onto a cookie sheet. I figured that would facilitate quick freezing on the bottom of the bag while leaving the top to freeze last.