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Author Topic: Why does paint change colour as it dries?  (Read 3802 times)

paul.fr

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Why does paint change colour as it dries?
« on: 03/05/2007 22:19:28 »
You can now buy a paint that goes on pink, but dries white. How does that work?
« Last Edit: 04/09/2007 21:42:37 by chris »


 

Offline daveshorts

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Re: Why does paint change colour as it dries?
« Reply #1 on: 03/05/2007 22:42:31 »
Could be something chemical - lots of things change colour with the addition of water - Colbalt chloride goes from blue to pink, anhydrous copper sulphate goes from white to blue. All you would have to do is find a chemical that will give up its water relatively easily as it dries.

The reason paint normally gets lighter as it dries is that the refractive index of the solvent is quite similar to the particles (normally TiO2) in the paint. This means that the light sees quite a flat surface as it enters the wet paint so it doesn't get reflected in lots of directions. When the paint dries there is no more solvent so the paint is now just a pile of little particles and pigment so the light gets bounced off in all directions, and looks whiter.
 

Offline elegantlywasted

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Re: Why does paint change colour as it dries?
« Reply #2 on: 04/05/2007 03:30:13 »
All I have to say, colour changing paint is a godsend when it comes to painting a ceiling!!
 

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Re: Why does paint change colour as it dries?
« Reply #2 on: 04/05/2007 03:30:13 »

 

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