Why are only some parts of this ice block cloudy?

[Wrichik Basu]

I had a sprain in my leg a few days back. The doctor recommended dipping my foot alternately in ice-cold and hot water to aid blood circulation. It is here that I discovered something interesting.

The picture above shows the piece of ice that was put in the bucket. The above picture shows the ice cube from above.

If you look at the large piece of cube from the side (see below), you can see that the upper part of the cube, that was near the open surface of the container in which the ice froze, seems to be almost transparent and has a crystalline appearance. The lower part does not have this appearance, and it is white and opaque.

Why is there a difference in the layers of ice in the large cube? Is it because the water was from tap and not completely pure? The water was put in the refrigerator for a period greater than 12 hours, so the ice has frozen properly. Can anyone explain this unique structure of ice? I've never seen this before.

 

[kuruman]

The cloudiness in ice cubes is due to small air bubbles trapped in the ice that scatter light. The air bubbles come from the air that is normally dissolved in the water. Beer foam also appears white even though the beer may be amber or even dark because the small bubbles in the foam reflect the incident light in all directions. A well known trick for making clear ice cubes is to boil the water before freezing it. Boiling drives out the air that is dissolved in the water.