How to Make Clear Ice – Part One

Darcy O'Neil :: December 28, 2009 11:14 PM

The perfectly clear ice cube seems to be the crowing glory on a well crafted beverage. Instead of a foggy opaque drink, a clear ice cube makes the drink sparkle and shine. Camper English (Alcademics) has been on a serious quest to find the occult formula to produce crystal clear ice. In his latest attempts he managed to shoe-horn his way into making some clear ice, though inefficiently.  That's not bad, it just doesn't answer the question as to what are the requirements to make clear ice and how it is really done. To figure it out we need to take a scientific look at the physical properties of water.

I like science, but physics was my most despised subject. I actually like the observation part, I just hated the math. If you've ever taken calculus and wondered where would a person use all those convoluted equations, physics would be the answer. Observing the physical world can help answer a lot of seemingly difficult questions, like why it is difficult to make clear ice? Many times we humans repeat the same action multiple times in the hope of getting a different result. Instead, we need to observe the results and think about doing things differently. A corporate execudroid would call that "thinking outside of the box".

We all know that ice floats, but the reason why it floats is because--unlike every other natural material--water becomes less dense when it goes from a liquid to a solid. The interesting thing is that life as we know it wouldn't exist on this planet if this didn't happen.

In the alterverse where ice sinks, it would just keep collecting at the bottom of the oceans since a couple hundred fathoms below the surface it's a tad bit chilly and ice would not melt. Any fish the were around are now crushed between layers of ice or lying around like fish sticks on the surface. If ice didn't float the oceans would be one giant hockey rink.

Floating ice is the giver of life, yes, but for clear ice it is a problem. In a container, like an ice cube tray, the ice will form at the surface creating an enclosed space. Five of the container's walls are plastic and the sixth is the ice surface. This means that the remaining liquid water is trapped inside this "box" and water does not like to be confined and gets very angry--almost Incredible Hulk type angry, but doesn't turn green. Why green by the way, you'd think something with anger management type problems would go red. Anyway....

If you've been paying attention then you'll remember that water expands when it freezes. In a confined space this means the remain liquid water is going to expand and push on the containers walls with tremendous force when it freezes. The transition from liquid water to solid ice at -2°C exerts a pressure of 10^8 pascal (14,500 psi). As many people know this is enough pressure to rip metal pipes apart.

For small quantities of water used to make ice cubes and ice blocks, the water will usually start freezing at the surface and then from the outside-in. The outside layer of ice is usually crystal clear because any dissolved gases and minerals or particulate matter stay in the liquid portion of the water. As the ice increases in thickness it begins to corral all of the impurities into the center of the block. Dissolved air and unfiltered water will cause a cloudy core, but impurities are not the main reason why ice cubes are rarely crystal clear.  

This expansion pressure is what makes ice cloudy in the center, not minerals and other debris. The visual flaws are caused by fractures in the ice when the last remaining liquid water in the center of the cube freezes and exerts a massive amount of force on the surrounding ice. The cube is basically cracked from the inside out.

Air entrainment does create bubbles and voids in ice, but even water devoid of dissolved gasses with still fracture. Boiling water does help to remove dissolved gases and improve clarity, however it will not remove minerals. Heat is more likely to dissolve extra minerals in the water, so make sure you clean your kettle regularly.

Now that we understand the problem what can we do to make clear ice? That will be the next post, as I'm still waiting  for the ice to freeze. But I will give you a hint: we need to freeze the water from the bottom up. To do that you will need: 8 ft of copper pipe, a cookie sheet, tin-snips, a bag of nails or iron shot, a garbage bag, an aquarium pump (powerhead), a medium sized plastic container, a hammer, drill and a coat hanger. Art of Drink is a low budget production so I often call upon the powers of MacGyver to get things done! Now lets hope it works.

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