How to temporarily ‘fossilize’ a soap bubble

In very cold conditions, freezing a bubble can be done — although not always easily

The author temporarily mummified this soap bubble with the sub-freezing temperatures he encountered on a Minnesota afternoon.

M. Cappucci

Bubbles are fleeting, floating orbs of glee that drift lazily with the breeze. They dance dizzily for a few seconds, then POP! They burst in a sudden shower of soapy spittle. Unless, that is, you temporarily freeze them. 

Spheres have the smallest ratio of surface area to volume for any three-dimensional shape. So bubbles can trap the most air of any form made from a soapy solution. The bubbles’ walls also are amazingly thin — usually only a few millionths of a meter thick. (That’s about a fiftieth the diameter of a human hair.)

That thinness helps them freeze. At temperatures from –17.8º to –12.2º Celsius (0º to 10º Fahrenheit), the bubbles can freeze in about 15 seconds. Take it down below –23 ºC (–10 ºF), and they freeze in 10 seconds or less. So for people who find themselves in a frigid setting, this can be a fun project to try.

The large quantity of cold air inside a bubble effectively cools the walls as the outdoor air chills the exterior. That exposure to piercing cold from both sides speeds up freezing. It’s the same reason bridges ice up faster in cold weather than on nearby patches of asphalt on the ground. 

Wind also helps. It’s due to what’s known as evaporative cooling which is what makes damp laundry on an outdoor clothes line dry faster on windy days. As an object dries, it cools. That’s because the evaporation of moisture uses up heat — thermal energy. When more air passes over the bubble, it eats away at excess moisture on the bubble’s surface. That causes more cooling. The windier the day, the more exaggerated this effect can become. Keep in mind, though, that the wind also can stress a bubble’s wall to where it risks popping.

Near the ground, swiftly moving air currents can cause small eddies. Generally invisible to the eye (unless they’re twirling leaves or snowflakes), these tiny whirlwinds can develop just about anywhere. If they become too turbulent, they can break a fragile bubble. That’s why it’s helpful to try freezing a bubble when any winds are light, at most. The optimal speed is 1 to 3 kilometers (0.6 to 2.5 miles) per hour.

With all this in mind, if you find yourself (as I did) in a very frigid environment, you can try your hand at “fossilizing” bubbles. As my video shows, it’s a cool trick, but sometimes a challenge to pull off. So wear heavy gloves and remain patient. 

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