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I want to make some ice cubes that are large (1" on a side or more), crystal clear, and perfectly cubical. I want them large to make my drinks dilute less slowly, and clear and cubical because I think it looks nice. When I make ice in the freezer, it's always cloudy. Any ideas?

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Wired Magazine had a recent guide on how to make crystal clear ice. I'm copying it here since the article says it's under Creative Commons license:

Go Big Ditch the ice tray and use a large vessel like a thick plastic bowl or, better yet, an insulated cooler. Fill it with water and stow it in the freezer.

Wait The H2O can take a day or so to solidify. Remove the mini berg when it’s solid on the outside but still has a liquid core.

Drain With an ice pick, bread knife, or screwdriver, make a hole to release the trapped water.

Segment Score a grid onto the slab of ice, then pry it apart into cubes - the ice should break cleanly along the seams. Bigger cubes are ideal because they melt more slowly.

Contributed by Camper English

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    Aha! This is why commercial ice cubes are usually hollow!
    – drxzcl
    Oct 2, 2011 at 21:45
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The cloudiness is caused primarily by impurities. Use distilled water and boil it twice, letting it cool between each boil. This removes all impurities and will result in clear ice. The second boil may be unnecessary, but it can't hurt. Make sure you keep the pot covered while it cools.

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    I have tried this and I could not get clear cubes.
    – papin
    Jul 24, 2010 at 3:58
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    You need to make sure there are no other impurities so impurities in the ice cube tray, anything that falls into the ice cube tray whilst it is freezing, including any other ice and andy rough edges on the ice cube tray will allow potentially allow a crystal to form as well.
    – Ian Turner
    Jul 25, 2010 at 8:22
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    Water freezes from the outside in. And it expands when it freezes. Put these two ideas together, and you understand that the pressure created by the expanding water inside is what screws up the perfect clear crystals, not impurities. Aug 8, 2010 at 2:51
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I see there's a checkmark, but just as a possible option - if you're talking about non-alcoholic drinks, what about making ice cubes of the same liquid - like some people do with lemonade ice cubes? They still might be visible, but you'd certainly have less dilution.

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I hooked up a Reverse Osmosis system to my fridge and now the ice is clear except for some air bubbles. If I wanted to make some "party ice" I'd use RO water but I would let it sit out for a while before putting it in the freezer to get rid of the air bubbles.

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Dave Arnold says that ice must freeze from the bottom to be clear.

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Another way to remove impurities from water is to just let it sit. Fill a bowl with water and cover it. Come back a day later and ladel the water from the top.

Impurities tend to sink to the bottom, but it takes quite a long time.

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try breaking the crystals every time they begin to set. once you have the start rebreak the cubes. this will also remove any air bubbles which can cause the cloudiness.

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The cloudiness comes from air in the water. Unscrew the aerator from your faucet before filling your container.

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I believe the trick that commercial ice makers use to make clear ice is to constantly agitate the ice while it freezes.

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    I've heard that too, although I saw an episode of Mythbusters where constant agitation failed to produce clear ice. Possibly it needs to be combined with the distilled water/boiling method that hobodave suggested. Aug 8, 2010 at 12:24

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