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Be careful not to put too little water in the bowl or the freezing will release enough heat to warm up the salt water to 0°C before the ice cubes finish freezing. The colder the freezer is, the higher the concentration of salt needs to be to prevent the salt water from freezing. You will learn from experience how much salt is needed for the temperature you normally set your freezer to.    The result is bubble free ice that is strong and crack free because it froze without any trapped regions of water ever forming during the process.
Fill up a bowl with water then dump a lot of salt into it to prevent it from freezing then put it in the freezer. Leave the salt water in the freezer at least 3 hours to get really cold. Boil some water, then let it cool to eliminate microscopic bubbles. Take the bowl of salt water out of the freezer to prevent the water in the ice cube tray from freezing from the top. Fill up an ice cube tray with water then float it on the salt water in the freezer which is denser than fresh water. Put the ice cube tray back in the freezer to prevent melting. Put the bowl of salt water back into the freezer so that you can skip the first step the next time you want to make clear ice cubes.