Why is lather of soap always white?

Answer 1

There are two things at work, here:

The first has to do with way the light that is reflected. The spherical bubbles reflect all colors, the achromatic sum of which is white. This is the same as a cloud on a sunny day, where water particles work the same way as the bubbles and give the cloud a white appearance.

The second has to do with the density of the particulate in the water; keep in mind that, other than the particulate floating in the water, the water itelf is clear. Once it is broken down to a foam, the colored particles are diffused. This is the same as grinding up a colored substance; if you grind it fine enough relative to the particles which color it, it will turn white.

Answer 2

There are two things at work, here:

The first has to do with way the light that is reflected. The spherical bubbles reflect all colors, the achromatic sum of which is white. This is the same as a cloud on a sunny day, where water particles work the same way as the bubbles and give the cloud a white appearance.

The second has to do with the density of the soap; once it is broken down to a foam, the colored particles (in this case, dye) are diffused. This is the same as grinding up a colored substance; if you grind it fine enough relative to the particles which color it, it will turn white.

Please see Color and Foam in Nature by David K. Lynch, William Charles Livingston: [related link]

Answer 3

The white color of soap lather is due to the scattering of light by the tiny air bubbles trapped in the lather. As light passes through the lather, it is reflected and refracted multiple times by the bubbles, which gives it a white appearance.

Answer 4

See related question for the answer.

Answer 5

The surf :)