If you've ever looked into making clear ice for drinks, you know that there are all sorts of assertions about needing to boil the water first, or using filtered water, or you need a special clear ice maker.
According to Nick, the Cocktail Chemist, in this video, all you need is a small 6-pack cooler with the lid removed.
Thanks to directional freezing, all of the impurities (clouding, bubbles) will settle to the bottom of the open cooler as you freeze it and the top section of the resulting ice block will be clear. You then simply remove the block and cut off the bottom part to have a clear block of ice remaining.
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