Wednesday, February 23, 2011

a year without ice

For the first time in several years, Lars and I are sitting out of the World Ice Art Championships. I'm rather busy with other things this year, and Lars would have had even more difficulty than usual taking time off work. I'm pretty sure we'll be back at it next year, but this time I'm enjoying watching the Single Block Classic web cams from far away in Colorado.

Of course, this winter hasn't been entirely without ice. I haven't picked up a chisel yet, but Lars made a few sculptures (with help from Celso) for his school's winter ball, and both of us have started experimenting with new methods of producing our own ice for carving.

For sculpting, it is almost always desirable to have very clear ice, not white ice, but making a sizable chunk of clear ice is tricky. The problem is that liquid water contains quite a bit of air and often some sediment or other impurities that become more obvious when frozen. As the ice forms, the crystal structure forces the air into pockets that become large enough to see, and all those little bubbles make the ice white. White ice is often unappealing visually, and it is structurally weaker.

The most common technique used to produce commercial carving blocks is to continuously circulate the liquid water as it cools, keeping the top surface in particular from freezing before the rest of the block does. Without this recirculation, ice naturally forms on the top surface first, forming a barrier that prevents air from escaping the rest of the block. Lars had the idea that, instead of recirculating the water, we could keep the top surface from freezing first by simply heating it directly. Here you can see him extracting a large block from the giant "Ice Cube Tray" in his yard. I believe he used a small aquarium heater to do the job, and he was pleased with the result.

I want to try the same thing in Colorado, but I don't have weather so cold as Lars does in Fairbanks. I am afraid that a simple aquarium heater might produce too much heat, but I will give it a try. I figure the worst case scenario is that I have to build my own temperature control device. Not wanting to handle ice cubes as big as Lars's, I picked up a 20 gallon trash can for my experiment. I didn't even have a simple heater when some particularly cold weather came to town recently, so I just filled the bin 3/4 full of well water and set it outside to freeze. This is so I'll be able to compare subsequent results with heating to the result without heating.

As you can see from the block of ice split in twain, the result was terrible. Not only was the entire block full of tiny air bubbles, but a large air pocket formed in the center. When mostly clear ice has a central region with lots of little bubbles, that region is called the "feather." This is far worse. Interestingly, I didn't even have to split the ice myself. I pulled it out of the trash can on a relatively warm day and only looked at the surface. A day or two of above-freezing temperatures later I found that it had split apart on its own!


anithri said...

Mossman makes ice interesting, so is now, officially, the most interesting person I know.

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