Why is the middle of ice white?

[Golshan]

Hi,
This is my question:
why is in the middle of ice, white ?
(have you noticed ?)
I guess the reason must be that water molecules don't have enough space to expand naturally and form symmerical crystals; and the white colour is because of this disarrangment in water crystals. Is my guess true ? So, how can we make a piece of ice that is fully transparent ?

 

[Astronuc]

If the ice is opaque, that can be the result of air dissolved and/or impurities in the water which are then entrained in the ice. Boiling water to remove air and then cooling/freezing the water, especially under compression will help to make clear/transparent ice. In some ice sculptures, one can see transparent ice.

 

[Andy Resnick]

The ice is milky white due to air bubbles- dissolved air comes out of solution upon freezing.

To make clear ice, de-gas the water first.

 

[Golshan]

to Andy Resnik:
so why just the center of ice is white ?

 

[Andy Resnick]

I would think that as the water freezes in the periphery of the container, the dissolved air moves toward the liquid phase (segregation). Once surrounded on all sides by ice, the air is trapped.