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University of Bergen
Geophysical Institute

24 days of kitchen oceanography

Each day a new experiement will be posted here. Reveal what is hidden behind the windows by clicking on the arrows below.

Introduction
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Day 10
Day 11
Day 12
Day 13
Day 14
Day 15
Day 16
Day 17
Day 18
Day 19
Day 20
Day 21
Day 22
Day 23
Day 24

Main content

Colored ice cubes

Day 19
19.12.2020

Why is the ice cube clear at the edge and colorful in the middle?

Fargede isbiter
Photo:
Mirjam Glessmer, GFI

Experiment 19:

When we freeze water dyed with food coloring, it can’t freeze into a homogenously dyed solid, because the color can’t be integrated into the crystal structure of the ice. From the outside, where the cooling of the ice compartment attacks, ice forms which consists only of water molecules. The color is increasingly concentrated and pushed back into the – still liquid – interior of the ice cube. When the freezer is cold enough, the colored core will also freeze, but it will form much more irregular ice, because the color disturbs the uniform crystal structure.

Chapter 19: Colored ice cubes

In the freezing process, the salt is "rejected". The freezing water molecules create a uniform crystal structure, and the remaining salt water is forced into pores and to the edge of the ice, where it is released into the surrounding water and sinks. Sometimes however, small reservoirs of concentrated salt water are trapped in the ice. Sea ice therefore has a sponge-like structure.