Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Steve Kale
<stevekale@b...> wrote:
>
> I think one would classify this as a "dye" ink although the border
between
> dye and pigment is getting blurred and there have been advances in dye
> longevity.  We once debated here, and I don't think we at all
resolved the
> issue, the question as to at what point does a pigment become a dye.
 I'm
> not a chemist but I would like to know a little bit more about this
sort of
> thing in lay terms. 

Pigment ink (inkjet pigment, that is) could actually be called "dye
ink", but I suspect that corporate marketing considerations have
caused this fact to be obscured (it being too confusing for the
consumer to hear that organic dyes are also used to make these
pigments). Better to have us think in terms of finely ground, immortal
mineral pigments; of Raw Umber and Burnt Sienna and the like. But of
course it ain't so.

In the case of inkjet pigments, the organic dye molecules are not
truly dissolved but rather caused to become aggregated (combined) into
small, *solid* particles--i.e., tiny crystals each containing
thousands of molecules. These dye particles can be kept in a stable
liquid suspension (i.e. kept from clumping together) by forming a thin
layer of a protective polymeric resin (or other stabilizers) on the
surface of each particle. Dye molecules within these tiny crystals can
absorb light (i.e., be colored) in a similar way as the dye in true
solution. But not exactly the same.

Why bother with the extra work? It's because the dye molecules inside
those pigment particles can be considerably more stabile against light
and chemical degradation by virtue of being in a "solid state"
environment--rather than in solution-state (i.e., rather than being
"molecularly disperse"). The downside of using dye in the solid state
may be that the pigment dye is less "efficient"--i.e., has lower
optical absorption (optical density) than comparable amount of dye in
true solution (i.e., the so-called "dye ink").

Both kinds of dye can (conceptually at least) be combined within one
ink; a relatively small amount of free (dissolved) dye component might
serve to boost the color density (although possibly at the cost of
some loss in overall fade-resistance).

Phil