Re: Pigments vs Dyes


"Roger Breton" <graxx@xxxxxxxxxxxx> wrote in message
news:BEFD4330.10BDA%graxx@xxxxxxxxxxxxxxx
> I'm trying to understand the nature of dyes and pigments. Is it a fair
> statement to say that dyes are water-soluble whereas pigments are not?
>
> I guess it's more complicated than that...
>
> Roger Breton
>

Roger,

You are on the right track. A dye dissolves in a solvent (not necessary it
be water) on a molecule by molecule basis. The size of the dye species is
less than 2 nm.

A pigment is an aggregate of molecules that might still be quite small (less
than 100 nm) so as not to give scattering. For organic pigments they can be
quite transparent even if larger than 200 nm if their refractive index
matches the medium they are supported in.

The distinction is important depending on the application.

mike



.

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