Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Color Mixing (Pigment) question



I think the idea that pigments lay side
by side, and therefore reflect both blue
and green (as opposed to absorbing both
blue and green) depends on your definition
of "pigment," how fine the pigment is,
and whether the main source of reflection
is the pigment itself or reflection from
whiteners in the paint or paper.

Most inkjet printers use soluble dyes.
Most water-color painters also use
water-soluble dyes. Do you include these
within the definition of "pigments" used
for "subtractive color mixing?" If so,
these do not lay side by side at a
macroscopic level. In these cases the
light travels through the transparent
(but colored) dyes and reflects from the
whiteners in the paper back through the
dyes. The pigments, i.e. dyes, are indeed
acting as stacked filters. If you mix
narrow-band blue dye and narrow-band
green dye and paint it onto white paper
you will not get cyan.

Even in the case of non-soluble pigments,
the pigment in good paint is extremely
fine, and a whitener (today almost
exclusively titanium dioxide) is the main
reflective agent. If the light is
essentially going *through* very fine
pigment, and reflecting from titanium
oxide or other whiteners (within the
paint or within the paper) then the
non-soluble pigments are also acting
like stacked filters.

Common inkjet printers use dyes (soluble
pigments). Photo-quality inkjet printers
use mostly dyes, but some high-end printers
use extremely-fine non-soluble pigments
because they are less prone to fading.

So... I think the big questions are...
what is the main reflective agent,
how fine is the pigment,
is light going through the pigment
to get to the reflective agent.

Michael D. Edmiston, Ph.D.
Professor of Chemistry and Physics
Bluffton College
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu