When I pulled out the ice tray to make a whiskey lemonade over the weekend, I couldn't help but notice that the ice had a cloudy white spot in the middle of it. This prompted me to ask: why is it that some ice I buy at the store is crystal-clear, but the frozen cubes at home in my freezer appear murky and white in the center?
Ice cubes develop cloudiness when water is frozen quickly. As ice begins developing on the surface of water, certain gases can no longer remain dissolved and begin to surface as microscopic bubbles. An already-developed outer layer of ice traps all the bubbles inside the frozen cube. Another reason for the white color may be traces of calcium carbonate or impurities, which are small and flaky in appearance but are completely harmless.
Ice makers are able to achieve a clear, see-through effect by distilling water, then freezing it in stages, and by using a mechanism that allows bubbles to be washed away as ice cubes develop.
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