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Weather science: Make frost at home!

07:00 PM
February 19, 2023

Weather science
Make frost at home!

An empty tin can is the main piece of equipment needed to make frost at home!An empty tin can is the main piece of equipment needed to make frost at home! - © picture alliance

It's been unseasonably mild winter across many parts of the eastern and central U.S., so if you're craving a piece of winter, why not try making frost at home!

All you need is:

  • A clean, empty tin can
  • Ice, crushed if possible
  • Water
  • Salt

Half-fill your tin can with ice, fill a quarter more of the can with water, then liberally sprinkle with salt. Cover your tin with a lid and shake gently to make your solution.

Wait a few minutes (though it can take up to ten) and watch your frost form! Generally the more salt, the quicker the process, while too much water can slow the process.

How does this work?

Frost is a thin layer of ice crystals which form on surfaces below zero, and below the dew point. This means moisture is present, so as air condenses in a sub-zero environment, it forms ice crystals on a surface rather than dew.

In our experiment, putting ice inside your can makes it very cold and the outside surface below freezing. Adding salt lowers the freezing point of water, causing the ice to melt. The water vapor in the air then condenses as ice crystals on the outside.

This process of using salt to lower the freezing point of water is exactly why we use it to treat our snow-covered roads in winter.

James West
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