Welcome to brain stuff from how stuff works, Hey, brain stuff, Lauren vocal bam here. When temperatures dip below freezing, it adds a number of extra hazards to driving, but perhaps none so tricksy as black ice. These are slick patches of ice that blend in with the black pavement beneath them because they're so transparent. When drivers blind to the danger steer their cars over the ice, they can lose traction and wind up in an accident. Other kinds of
ice are easier to see. You've no doubt noticed that homemade ice cubes usually look cloudy in the little opaque in the middle, like whitish blocks of cotton candy. That stands in contrast to the frightening clarity of black ice. So how come black ice is see through but the cubes in your typical ice trays are not. Liquid water appears to be clear. That's because the material neither absorbs nor reflects most of the spectrum of visible light. Most
wavelengths in the spectrum pass right through it. And that's right, I said. Most technical water is not colorless, although it often looks that way. Believe it or not, The liquid has a natural bluish tint, owing to the fact that it absorbs red, yellow, and orange light more easily than blue light. But our human eyes can only observe this azure quality in deep bodies of water. This helps explain why ocean water and glacial ice look blue to us,
while glassfuls of drinking water look transparent. Yet there is a deceptive quality to water. No matter how fresh and clear it may seem, it's never one pure. A sample of H two O might contain floating bits of organic matter like algae or plant remains, along with suspended sediments a dust particles, or flexi minerals like calcium and lime. It may also harbor lots of dissolved gases such as oxygen.
With outsid oxygen, fish wouldn't be able to breathe. Gases and physical impurities are the key to understanding why those ice cubes in your tray are so darn cloudy. When water freezes, internal debris and air bubbles can become concentrated. The class stirs impede light, causing all the differently colored frequencies on the visible light spectrum to scatter. When this happens, it makes the ice look white and clouded. But it doesn't always happen. Let's take for a case study, a
YouTuber who once appeared to walk on water. Thomas Nunnock filmed himself in a travel companion walking across vel k Hankovo place So, a deep freshwater lake in the Slovakian Mountains. His video went viral because it shows the two men standing on some unbelievably clear ice. The lake bottom rocks
below them are pristinely visible through the frozen water. The ice and Nunus video was so transparent that some viewers assumed the footage had been faked, but the phenomenon is very real, and when the lake freezes over, as it often does, the surface ice can be crystal clear. An ice sheet needs to be almost entirely free of both air bubbles and debris in order to have this degree of clarity. There are other requirements as well. Ice is made up of crystals, and when water eases rapidly, those
crystals tend to be small and numerous. That makes the ice look whider because each of those crystals have reflective surfaces, so if there are more crystals, there will be more reflection going on, which will help scatter incoming light on the other hand, ice that's been slowly frozen is built out of fewer and larger crystals, and those promote transparency. So ice will only be see through and crystal clear if it freezes slowly and doesn't have too many impurities
or crystals. Thomas knocks Now famous YouTube video is what it looks like when all these conditions are met. On the day of his trek, the lake was topped with an icy blanket that was around two centimeters thick. That's about three quarters of an inch. The water must have frozen gradually during a tranquil period with no strong winds to deposit debris in the lake or to churn up the water. We see the same kind of thing happening in roadway black ice, although not all of this stuff
comes from the same source. It can start out as fog, mist, drizzle, or melted snow. It always freezes slowly during low wind periods. It's consistently then, and it contains very few impurities. That's why black ice is so transparent and frustrating to motorists, but highway annoyances nonwithstanding, transparent ice isn't as common in nature as the white clouded variety. There are a lot of reasons why given ice chunk you find out in
nature might not be clear. Some ice is made up of fallen snowflakes whose angular shapes and regular crystals scattered light and sometimes temperatures drop rapidly, resulting in ice with those smaller crystals. Artificial ice is subject to these same physical laws. Most household ice trays are designed to freeze little blocks of water from the outside. In doing so has the side effect of driving impurities within the water towards the center of each cube. The finished products therefore
look white and hazy in the middle. To get clearer, more attractive cubes, some restaurants use expensive machines that freeze water very gradually and exclusively from one side that lets the impurities escape outward. Though if you want to make clearer cubes at home, you can do it on cheap. Try boiling the water first, thus ridding it of dissolved gases before the freezing process starts, and just blood it cool of it before you add it to your ice tray.
You wouldn't want to melt the plastic. Today's episode was written by Mark Mancini and produced by Tyler Clay. Shop for your favorite brainy companion in our online shop to public dot com slash brain stuff, and of course, for more on this and lots of other completely clear topics, visit our home planet, how stuff Works dot com