Transparent glass with air bubbles

Molecules, Water

8 things that are unusually white in nature

By Juman Hijab

Reading time: minutes

Original date: January 2, 2020  

Updated: February 10, 2023

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Transparent glass with air bubbles

By LVV. Transparent glass ball with air bubbles inside on a blue background. Shutterstock.com, 45809566

White color in nature

There is a simple explanation for much of the white color that we see in nature. Common things appear white because of entrapped gas molecules.

The common element creating a white color is gas bubbles held captive by the material. This applies whether the material is liquid (for example water) or solid (for example ice cubes , feathers, or snow).  In the image, it is glass that is entrapping air bubbles.


Here are 8 items that are pure white because of refraction of white light off a disorganized mass of gas bubbles, and several that are white due to other reasons.

Whipped egg whites

Scott Mindeaux. whipped_egg_whites. Flickr.com, July 6, 2005.

Proteins in egg whites hold air bubbles captive

Disorganized and different-sized air bubbles reflect white light back to us.   

Pockets of air are not only encompassed with water. Other natural materials hold air bubbles hostage. For example, molecules such as proteins from a translucent egg white that is beaten by a mixer can form pure white meringue.

White air bubbles beer

Martin Garrido. Beer. Flickr.com, Dec 27, 2011

Why is the head of a pint of beer white not amber?

Most of the time, the gas molecules are air molecules (oxygen  (O2) and nitrogen (N2) gas).

But other times, the entrapped gas is something else. For example, the gas that forms the beer head and the foam on a soda drink is carbon dioxide (CO2)

Fermentation proteins of beer forming the “head” of a pint of beer.  The gas that produces the "head" in a pint of beer is carbon dioxide, though nitrogen is sometimes added to produce a longer lasting, less acidic taste. 

Whipped cream

Brian Teutsch. Whipped cream. Flickr.com, Nov 22, 2007.

Keeping whipped cream stiff for days

Fats are also very good at holding air bubbles captive. There needs to be  at least 30% fat in cream to allow the fat globules to encompass enough air bubbles for a whipped texture.  


Whipped cream that lasts for days

Of note, if you add protein (which act as cohesive molecules) to the cream, this will help make the whipped cream keep its shape longer. This is because the proteins attach to the water layer of the milk and create molecular nets that also hold the air bubbles in place.  Examples include adding gelatin or non-fat powdered milk to the whipped cream mixture. 

Both techniques will result in whipped cream that has stiffer peaks that keep their shape for longer than 1 day.

Soapy foam on man's hand

By jocic. Soapy foam on man's hand. Shutterstock.com, 160713749.

kismihok. Bubble: Giant soap bubble and the sky before storm. Flickr.com,  July 17, 2012.

White versus transparent soap bubbles

Detergents/soap foams:  A white foam develops when we use soap to lather our hands. Contrast the picture of the white foam with its multitude of bubbles with the see-through single soap bubble shown above. 

 Soaps are very good at entrapping air bubbles. You could wash your hands with green soap, but the froth that comes out is white.  However, if you blow a single (or a few) bubbles, they will be transparent.

The reason is that with a limited number of bubbles, there are only a few interfaces allowing the light to go through without a lot of scatter.

Giant soap bubble

elPadawan. Giant Soap Bubble:, Můstek subway station, Prague. Flickr.com, July 12, 2012.

What is the biggest soap bubble one can make?

On another note, one can make single large bubbles that maintain their shape for a longer time. One way of doing this is through adding corn syrup to the soapy mixture.

Keep in mind that the netting that holds air bubbles in place - in soap, cream, or egg whites - contains a layer of water. When one incorporates a sugary molecular substance into that water layer, everything becomes many times more cohesive. 

The increased stickiness of the water layer allows the soap bubble to expand to considerable dimensions. 

Moreover, since the glucose molecules attract the water molecules, the soap bubble takes longer to dry out. It lasts longer without popping.  

Transparent glass with air bubbles

By LVV. Transparent glass ball with air bubbles inside on a blue background. Shutterstock.com, 45809566

Glass holding air bubbles captive

Even glass can trap air bubbles. When there is enough of them to cause a disorganized refraction of light, they will appear white.

polar bear white fur

Jessica Merz. Polar bear. Flickr.com, Feb 20, 2006.

Polar bear skin is black not white

Polar bear skin is not white. The hairs that make up the bear's fur are transparent and hollow; this fur covers a black skin! However, when sunlight hits a polar bear's fur, the light scatters from the air mass within the straw-like strands of hair. The result is a white coat.

White snow/white Mynah bird

Charles Barilleaux Bali Mynah. Flickr.com, March 31, 2014

Mynah birds have ultra-white feathers

Polar bears and Mynah birds have something in common. Their protective covering encases air pockets in translucent materials. Mynah bird feathers are not white: the feathers of the Bali Mynah bird tend to be hollow entrapping pockets of air. 

In both the fur and feather examples, the casing is made of protein molecules that are a form of keratin. This is the same protein that makes up our hair and nails.

Lake foam

James St. John. Lake foam along the shoreline of Storr's Lake. Flickr.com, March 24, 2007.

Sea foam and a beer head are white for the same reasons

The same concept - adding cohesive molecules to foamy liquids makes the foaming bubbles last longer - is the reason sea foam gets created.

Proteins from broken down biodegradable material, like algae, mixes with the water. Thin layers of protein and water hold innumerable bubbles in place. The result is a long lasting foam.

White snow white birch

Jevgenijs Slihto. Birch. Flickr.com, March 7, 2015

Butterfly wings, birch trees, and beetles

Keep in mind, that not all white things in nature are due to reflection off a bunch of gas bubbles. The microscopic structure and arrangement of the fibers can reflect light back to us, creating a structural white color.

Examples include:

In some of those cases, the actual material is colorless and transparent. However, because it scatters white light, it will appear white. In those 3 cases, air bubbles are not the reason for the white color.

Finally, some flowers create a pigment that echoes all light; , creating white flowers. 

Conclusion

In effect, disorganized interfaces that entrap gas molecules (like nitrogen N2 and Oxygen O2) reflect light. Keep in mind that air - like most gasses - is colorless. It doesn't absorb any wavelengths of light. Without a visible container encompassing gas molecules, the gas would be transparent.

Even if the substance holding the bubbles in place is transparent (like water), light can be bounced at the level of the interface. Some of the light echoes back to our eyes. This creates the whiteness, as if the bubbles were painted.

 "Whiteness" is produced depending on the level of chaos around bubbles. The more refraction (bouncing around) of light, the whiter the surface of the object will appear.


Tags

air, proteins, White


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