Former bartender here. Having nice cocktail ice chunks at home isn't as complex as this might make it seem. No need for a clunky box in your freezer or costly gizmos. I keep a travel-sized coffee thermos in my freezer with about 2-3 inches of water at the bottom. Takes 18-24 hours to create one chunk. If you time it right, 90% of the water freezes, and the water impurities pool at the bottom – pop out the frozen chun…
Water expands when it freezes, in my head thermos is an extremely rigid structure, how do you stop it from rapturing?
I've seen some other ideas like freezing water in a camping cooler with its top open.