Cloudy ice is NOT because of "impurities"

You know how the Internet can make something untrue fester into alleged fact? This is one of those things, and it drives me nuts.

Getting crystal clear ice is a neat bar trick that is typically achieved by freezing it in a directional manner. It's why ice on the surface of a lake is typically a lot clearer than what you'd find deeper. In your freezer, this can be achieved by putting the water in a deep container that's insulated around the sides, but not the top. If the upper half is separated by small holes, the top bits freeze clear, while the lower part is cloudy.

What almost every words-on-the-Internet say is that this is because it forces the "impurities" to the bottom. This is bullshit. If this were actually true, then the purest of distilled and filtered water would freeze clear in conventional ice cube trays. But it doesn't. Distilled water has effectively no mineral content. The reason has nothing to do with minerals or whatever people claim is in the water. It's because of gases. I imagine it's mostly nitrogen, oxygen and CO2 (i.e., air). It's the air that gets forced down in the directional freezing.

Seriously, every "article" or how-to says it's impurities, but unless you consider air an impurity, it just ain't true.