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  #1  
Old 11-19-2008, 05:56 PM
zisha zisha is offline
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How does colored soap become white?

Here's a question my kid asked me which had me stumped.

How does liquid soap and shampoo turn white when lathered no matter what color it was before and why doesn't the coloring agent stain the skin?
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  #2  
Old 11-19-2008, 06:30 PM
Q.E.D. Q.E.D. is offline
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The dyes used in liquid soaps are so highly water-soluble that they just dissolve away before they can stain anything. Plus, the concentration of dye in soap is fairly small; once in solution in water it's virtually colorless. To color soap bubbles and suds likethese requires a much higher dye concentration. In any case, ordinary soap suds appear white because the tiny bubbles which make it up all reflect swirls of numerous colors just like big soap bubbles do; all those colors combined appear white to our eyes.
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Old 11-19-2008, 08:21 PM
Sapo Sapo is offline
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WTH, please link to the recipe for those colored bubbles.
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Old 11-19-2008, 08:25 PM
Q.E.D. Q.E.D. is offline
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Quote:
Originally Posted by Sapo View Post
WTH, please link to the recipe for those colored bubbles.
This is the complete PopSci article.
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  #5  
Old 11-19-2008, 08:43 PM
Santo Rugger Santo Rugger is offline
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Can somebody verify or refute the veracity of this statement I've heard:

The numerous colors in big bubbles Q.E.D. speaks of are created because of the way a soap molecule works. It has a hydrophobic and hydrophyllic end. All the hydrophobic ends point away from the center of the sphere, and spread out as evenly as possible on the surface. By happenstance, these molecules are about 500nm long, which is the same magnitude as the wavelength of visible light. Therefore, the different colors you see are due, in part, to the refraction of light through the different thicknesses and angles of the bubble.
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Old 11-19-2008, 08:46 PM
Sapo Sapo is offline
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Super cool. Great read, thanks.

Hey, anyone remember those weird gummy bubbles you would make with a thin straw that you dipped in this foul smelling sticky mess? What were those called? Is it still available? Will I get brain and lung cancer at age 40 for having used those?
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  #7  
Old 11-19-2008, 08:49 PM
Q.E.D. Q.E.D. is offline
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Super Elastic Bubble Plastic. No longer available, as far as I can tell.

ETA: There still exist similar products.

Last edited by Q.E.D.; 11-19-2008 at 08:53 PM..
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  #8  
Old 11-19-2008, 10:17 PM
Chronos Chronos is offline
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Therefore, the different colors you see are due, in part, to the refraction of light through the different thicknesses and angles of the bubble.
Not refraction, diffraction. The light waves reflect off of both the inner surface and the outer surface of the film. For some wavelengths, the two reflected waves will line up, and you'll see them clearly. For other wavelengths, the reflected waves will cancel each other out, and you won't see them. Which is which depends on the precise thickness of the bubble, so as the thickness changes, the colors change, too. This is also what causes the colors in oil films on top of puddles, and is related to what happens in those cheap plastic-and-cardboard glasses that make everything look like rainbows through them.

Back on topic, snow is also white for much the same reason that suds are, because they reflect light in all sorts of directions from all of the fine details of the flakes/suds. If you look at a single snowflake close up, it just looks clear, like ice (which of course it is).
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Old 11-20-2008, 10:18 AM
zisha zisha is offline
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Thanks

Thank Q.E.D for that informative answer and that interesting tidbit about the colored bubbles. According to the Wikipedia article

An automatic reply e-mail from Spin Master Ltd. states that "Spin Master has no immediate plans to launch Zubbles Colored Bubbles. We thank you for your interest."[4] A call on January 15, 2008 to Spinmaster confirmed that they have no plans to pursue this product at all, and that they have released rights to produce Zubbles.

Any idea what the problem is?
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  #10  
Old 11-20-2008, 01:44 PM
Tom Tildrum Tom Tildrum is offline
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Quote:
Originally Posted by zisha View Post
Thank Q.E.D for that informative answer and that interesting tidbit about the colored bubbles. According to the Wikipedia article

An automatic reply e-mail from Spin Master Ltd. states that "Spin Master has no immediate plans to launch Zubbles Colored Bubbles. We thank you for your interest."[4] A call on January 15, 2008 to Spinmaster confirmed that they have no plans to pursue this product at all, and that they have released rights to produce Zubbles.

Any idea what the problem is?
It's the Lindsay Lohan problem. They'd have to switch the name to Zubbles Bubbles of Color.
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  #11  
Old 11-20-2008, 02:57 PM
Acsenray Acsenray is offline
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Also see this thread: Why does toothpaste always foam white?
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  #12  
Old 11-20-2008, 03:23 PM
garygnu garygnu is offline
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I complained colored bubbles weren't out yet over a year ago.
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