Home science experiment: crystal clear ice

Last weekend, thanks to some inspired planning on the part of my wife, we got a baby sitter and met up with some friends of ours at a bar in Somerville.

To most people who know me, the very idea of me going to a bar is rather humorous, but rest assured that this was not a local drinking hole.  It was a relatively hip (perhaps a bit less so now that they have had a customer like me) bar called Backbar attached to another high end restaurant.  It’s the sort of place with interesting appetizers and fancy cocktails.

One of the things I noticed about their cocktails was the exquisite presentation, including the ice itself.  Rather than just regular ice cubes, these were large, perfectly square, perfectly clear blocks.

I tried to photograph one, but the reflections of the flash don’t quite do it justice:

I was immediately curious about the ice; whenever I make ice, it comes out cloudy due to the  trapped air bubbles and impurities.  This ice, on the other hand, was completely clear, like a beautiful crystal.

I flagged down our server to ask, and he was very excited to tell me how it was delivered in large 20 pound blocks from an ice vendor, and then he and the other staff used extremely sharp knives to chop it up into smaller cubes for serving in the drinks (this apparently takes a great deal of skill not to injure yourself in the process).  However, since the ice already arrived in these crystal blocks, he had no idea how it was done.

Determined to find out, I did some research on the internet the next day.  The reason most regularly ice comes out so cloudy is that the outer edges of the cube freeze first, trapping the water with the air bubbles at the center.  Once the center gets cold enough to freeze, it expands, causing small fractures throughout the ice, which give it the cloudy look.

To get crystal clear ice, you need to get it to freeze on just one side using an insulated container.  As the ice forms, it pushes the air bubbles deeper into the container.  Eventually, it will form a cloudy chunk when the other end freezes, but if you remove it before freezing is complete,  you end up with a nice clear sheet.

I decided it was time for another one of our home experiments.  My past experiments have been around teaching my kids some principle, like the three states of matter, but honestly I was doing this purely for my own curiosity and hoping to entertain my kids in the process.

We filled a medium-sized lunch cooler (the kind of thing you would take to the beach) about 3/4 full with water and then put in the freezer with the lid open:

We then left it in the freezer overnight.  The cooler turns out to be a pretty good insulator, so only about a half inch on the top had actually frozen.  If we left it in for another day or two, we could have gotten a thicker sheet.  However, for the purposes of my experiment, it was good enough.

I dumped it upside down, and eventually there was enough give for the water to leak out, allowing the the sheet of ice to pop out.  Sure enough, it was crystal clear:

This experiment was much less educational than past ones, but my daughter was particularly very excited.  She asked if we could do it again tonight.  She went on to say that she loved experiments and wanted to do more of them.

Oh, the joys of parenting a four year old!  Some day I know that she will roll her eyes at the very idea of me trying to teach her anything (just as I did as a teenager), but right now she still has the excitement of a young kid.

I told her I would try to think of some other experiments we could try, and she asked if we could do one with scarves.  I explained the difference between science and fashion, but I think the distinction went a little over her head.

I’m excited that I created my crystal clear ice.  But I’m more excited that my kids are perhaps learning to see some of the wonder in the world that surrounds them, just like I do.



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1 Response to Home science experiment: crystal clear ice

  1. LuQ says:

    The other option is to boil the water (filterered, preferably distilled water) first, then freeze. Here’s a random page that explains this process (but can search on “boil water clear ice” to find many other matches): http://www.instructables.com/id/make-crystal-clear-ice!/

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