From: lva (lva@pamho.net)
Date: 10/01/01-01:53:26 PM Z
> On Mon, 1 Oct 2001, Richard Sullivan FRPS wrote:
> >
> > The issue of the pigment grind comes up. The fineness of grind in
> > general determines the color. As the grind goes finer the pigment
> > grows paler. Case in point: grind some cherry Life Savers in a
> > mortar. The finer you grind it the paler it gets. As stated before
> > ball milling only makes the pigment disperse into solution better.
>
> I doubt this analogy holds... put the "fine grind cherry life saver"
> in a few drops of water or gum arabic either & I assume the color
> would return.
>
> Have you tested change in color with grind in pigment?
I have. In some cases the change in color is stunning. For example, the
finer I grind the real Caput Mortuum powder pigment, the more colorful
and violet it gets.
But, as so often in this world, there's a downside. At one point a
pigment doesn't gain anymore by fine-grinding. It gets stale, lifeless.
Dr Kremer has his own explanation for this. He thinks--and he points out
that this is his personal opinion and not scientifically proven--that
the human eye can perceive individual particles down to 10 micron. If
you have ever seen a 10 micron line field (there's a test strip for the
Cromalin process, for example), it looks grey and you cannot make out
the lines. Kremer says while you cannot see them, you 'perceive' them.
I'm not sure. But the possibility is there.
Moist watercolor in tubes often consists of pigment particles between 0
and 1 micron. That is VERY fine. Powder pigments usable for the gum
process have particles between 0 and 20 or 30 micron. Kremer says the
light effect these pigment "mountains" or rather pigment "rocks" create
on the paper give life to the color. He may be right.
> How do you figure "fine grind" anyway? Are there absolute measures for
> pigment particle size?
Yes. In micron. There are technical sieves with known hole sizes.
Sieving pigment through such a filter gives one a pretty clear
indication of the coarseness of the filtered pigment.
Brahma
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