Expert: Daniel Mazur - 3/24/2008

Question
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 ?
and at last, I want some resources for furthur reading. (actually, I don't know in what kind of books I should look for it. is it part of optics ? or crystalogy ? ...)  

Thank's a lot

Golshan
Tehran, Iran

Answer
Hello,
ideal ice crystals are transparent like glass. The white, "misty" character is present in many real ice crystals, because they are not perfect. What you describe is most frequently a result of tiny air bubbles that were trapped in the ice during freezing.
How to make a bubble-free ice? This is hard, because water usually has a lot of air dissolved in it. It also contains dissolved minerals, which will cause their own share of ice crystal imperfections. For the latter reason I'd recommend starting with de-ionized water. I think that one approach would be to outgas the water by bringing to near-boil (maybe 90 deg.C) and carefully releasing air bubbles from the sides of the container. Then let it quietly cool down and then freeze in that same container.
Well, at this point I googled "how to make transparent ice" and there have been a few nice methods in the results. I recommend you do that. It may tell you more than study from books.
Did you know that there are about 10 different phases of ice? Ice is a very complicated material, albeit it is one of the most common things in our lives. Books on crystallography tend to focus on properties of ideal crystals, properties of non-ideal ones (like ones with air bubbles in them) are too specialized topics. Crystalogy (gemology) will hardly tell you anything much about ice, for it focuses on stones, gems. And finally optics would study the *effect* of the bubbles (lower transparency on all visible wavelengths), not the *cause*. To sum up, each one of these might give you a bit of interesting information, but none will give you a good, thorough lecture on how to make transparent ice. I seriously suggest that you look for monographies on ice and try to learn from them.
Take care,
Daniel