The throats of many hummingbirds appear to change colour when they move. This is because they are iridescent. Ever seen colours in soap bubbles? That’s a typical example of iridescence.
The throats of many hummingbirds appear to change colour when they move. This is because they are iridescent. Ever seen colours in soap bubbles? That’s a typical example of iridescence.

© Musée de la nature et des sciences de Sherbrooke 2007. All rights reserved.

The colours of most animals are drab and pigmentary in origin. Pigments create the animal's colour through the absorption and reflection of part of the light spectrum.

The very vivid colours that are seen in some animals, including hummingbirds, are not caused by pigments, but have a physical or structural origin. The colours depend upon the angle of incidence of the light and the refractive index of the structure. The thin scales on a hummingbird's throat or a butterfly's wings create light interference that results in iridescent colours.

Many insects, fish and shellfish have iridescent colouring.

The colours of most animals are drab and pigmentary in origin. Pigments create the animal's colour through the absorption and reflection of part of the light spectrum.

The very vivid colours that are seen in some animals, including hummingbirds, are not caused by pigments, but have a physical or structural origin. The colours depend upon the angle of incidence of the light and the refractive index of the structure. The thin scales on a hummingbird's throat or a butterfly's wings create light interference that results in iridescent colours.

Many insects, fish and shellfish have iridescent colouring.


© Musée de la nature et des sciences de Sherbrooke 2007. All rights reserved.

* a deep plate

* a straw

* liquid soap

Musée de la nature et des sciences de Sherbrooke

© Musée de la nature et des sciences de Sherbrooke 2007. All rights reserved.


Step 1: Soap please

Place some liquid soap in a deep plate.
Step 2: Make a bubble

Dip the straw into the liquid and gently blow through it to create a bubble.
Step 3: Watch it

Look at the bubble's colours as you blow. Stop blowing for a moment and quickly place your thumb on the end of the straw while you study the bubble from different angles.
Step 4: It's going to pop!

Here, the goal is to observe the colour change that takes place just before the bubble pops. Go ahead, blow gently.

Step 1: Soap please

Place some liquid soap in a deep plate.


Step 2: Make a bubble

Dip the straw into the liquid and gently blow through it to create a bubble.


Step 3: Watch it

Look at the bubble's colours as you blow. Stop blowing for a moment and quickly place your thumb on the end of the straw while you study the bubble from different angles.

Step 4: It's going to pop!

Here, the goal is to observe the colour change that takes place just before the bubble pops. Go ahead, blow gently.


© Musée de la nature et des sciences de Sherbrooke 2007. All rights reserved.

Step 1: Soap please

Step 2: Make a bubble

Step 3: Watch it

Step 4: It's going to pop!

Musée de la nature et des sciences de Sherbrooke

© Musée de la nature et des sciences de Sherbrooke 2007. All rights reserved.


The thickness of soap film varies from 0.01 micron to 1 micron (10,000 to 100 times thinner than a sheet of paper). Its thickness is greater at the base of the bubble due to gravity. The light absorbed by a soap bubble is reflected and splits into various colours depending upon the thickness of the film. Because the surface is thin, there is a lot of interference between the light absorbed and the light reflected, creating iridescence. When the upper part of the bubble becomes very thin, the interference prohibits the light from exiting and dark colours appear. This is a bit like what happens when a hummingbird is no longer in the angle of light, interference cancels the light from exiting and the bird's throat appears dark-coloured.
The thickness of soap film varies from 0.01 micron to 1 micron (10,000 to 100 times thinner than a sheet of paper). Its thickness is greater at the base of the bubble due to gravity. The light absorbed by a soap bubble is reflected and splits into various colours depending upon the thickness of the film. Because the surface is thin, there is a lot of interference between the light absorbed and the light reflected, creating iridescence. When the upper part of the bubble becomes very thin, the interference prohibits the light from exiting and dark colours appear. This is a bit like what happens when a hummingbird is no longer in the angle of light, interference cancels the light from exiting and the bird's throat appears dark-coloured.

© Musée de la nature et des sciences de Sherbrooke 2007. All rights reserved.

You can observe iridescence by placing a thin film of oil on water or by studying a CD, DVD or paper money. Iridescence is a way of inspecting bills for counterfeiting.

Musée de la nature et des sciences de Sherbrooke

© Musée de la nature et des sciences de Sherbrooke 2007. All rights reserved.


Learning Objectives

The learner will:
  • record observations about the experiment

Teachers' Centre Home Page | Find Learning Resources & Lesson Plans