Gases are more soluble in cold water. When it freezes, trapped dissolved gas molecules are visible to us as tiny bubbles in the ice cubes, or as cloudy looking ice cubes. Conversely, gases are less soluble in hot water; in fact at boiling point, the gas molecules escape from water together with the steam.
When water is boiled repeatedly (or continuously for minutes after it first comes to a boil), all the gases are expelled. Clear looking ice cubes are formed when this water is subsequently cooled and frozen. If there is any cloudiness in them, it is likely to be caused by dissolved minerals and dust. So if you want even clearer ice cubes, start with filtered or distilled water, which have less minerals and dust.
Clear ice cubes not only look prettier, but they also melt more slowly because there are hardly any air bubbles that expose a greater surface area of the ice.
Second Helpings
Thinking of preparing a special drink for a special someone? Concoct a pretty iced drink that stays colder longer by making and using clear ice cubes!
photos: in order - istockphoto/yvdavyd; depositphotos/mr_Brightside; jag_cz