Last year, I took a number of vacations which involved cruising, diving, snorkelling and walking on glaciers. Thinking back on those trips, I could not help but notice that water and ice exhibited different colours in different settings. I decided to dive deeper into the colours of water. Finally, here are my findings.
Water’s True Colour
The colour of an object mainly depends on the colour of light emitted from it. In the case of water its colour is also affected by factors like light source, absorption, scattering, and suspended materials. Absorption by water is stronger for red light, but weaker for blue light. Water is therefore, intrinsically blue. However, this effect is only apparent when the water is reasonably deep. This is why a glass of water appears colourless whereas a big aquarium looks bluish through the thickness of water.
Why is the Sea Blue?
Waters with Special Colours
The colour of water is also affected by what it contains. Suspended materials affect the colour of water. Sea water will appear green when it contains large amounts of green algae. Muddy water has a brownish yellow tinge.
Thin layers of ice and snow reflect light quite thoroughly, hence often appearing white. When walking on Franz Josef Glacier in New Zealand, I noticed that the ice was blue. Like water, light is scattered and absorbed in thick ice. The longer the path light follows to reach the surface, the bluer the tint.
The purity and age of the ice also play an important factor in the colour of glacial ice. As the ice ages it is compressed, melted and frozen again eliminating air bubbles that scatter the light rays and bounce them back out in the same white colour they entered. Once the ice becomes pure the light waves are much more likely to be absorbed, hence, promoting the deep blue shade.