Coloured Ice

Last updated on September 16, 2023

Exploring the Phenomenon of Coloured Ice

Have you ever taken a winter walk and come across a frozen pond or a patch of ice that seemed to emit vibrant colors? This captivating natural phenomenon, known as "coloured ice," has intrigued many observers. In this article, we will delve into the science behind this optical spectacle and explore the factors that contribute to its occurrence.

When light interacts with ice, it undergoes a fascinating process called birefringence. Ice, being a crystalline substance, has the ability to split light into two polarized rays that travel along slightly different paths. As these rays merge back together, they interfere with each other, resulting in various colors becoming visible to our eyes.

To observe this phenomenon in action, you can use a polarizing filter. A camera filter or even an old polarizing lens from sunglasses will suffice. Simply view pieces of ice through the filter while adjusting the viewing angle. As you do so, pay attention to any changes in color. You can also rotate the filter to see if different hues emerge.

Interestingly, the intensity and variety of colors in coloured ice are influenced by several factors. One crucial factor is the presence of an air layer beneath the ice slab. When light passes through this air layer before reaching the ice, it interacts with the surface differently, leading to the brightest and most vibrant colors. The thickness and uniformity of the ice also play a role in determining the color display.

It is important to note that the colors we observe in coloured ice are a result of selective absorption and interference of light waves. As light enters or reflects internally within the ice, certain colors are absorbed while others are allowed to pass through. This selective absorption, combined with the interference between the polarized rays, creates the mesmerizing array of hues that we perceive.

While coloured ice is often encountered during winter walks, it is not limited to natural settings alone. In fact, photographers like Andrew Kirk have successfully captured stunning images of coloured ice on overcast days using a single polarizing filter on their cameras. These images serve as a testament to the beauty and versatility of this natural phenomenon.

In conclusion, coloured ice is a captivating optical phenomenon that occurs due to the birefringence of ice. Through the interaction of polarized light rays and selective absorption, a dazzling array of colors is revealed to the observer. Factors such as the presence of an air layer beneath the ice and the thickness of the ice contribute to the intensity and variety of colors observed. So, next time you find yourself on a winter walk, don't forget to bring a polarizing filter along and immerse yourself in the enchanting world of coloured ice.

Ice Colours

Imaged on a frozen pond December 20 by Andrew Kirk.

©Andrew Kirk, shown with permission.

When on winter walks take a polarizing filter with you - A camera filter or a lens from some old polarising sunglasses will do. View pieces of ice with the filter, adjusting the viewing angle as you do so. When colours are seen rotate the filter to see if they change.

Andrew Kirk imaged his on an overcast day using a single filter on the camera.

The colours are produced because ice is birefringent. Light entering or internally reflected is split into two polarised rays which have slightly different paths. When viewed with an external polariser the two rays interfere. Some colours are darkened leaving other hues shining brightly.

An air layer beneath an ice slab yields the brightest colours.

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Reference Atmospheric Optics

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