Digital Prints

216
Mastering Digital Printing
The main advantage of pigment inks is that, in general, they are more stable than dyes,
being more lightfast and less sensitive to environmental gases. Why? Due to the relationship
between surface area and volume, the smaller the particle size, the greater the relative
surface area, and the more likely that a photo-fading agent like light or a chemical attack
agent like ozone can reach it. Since pigments are more complex with many more molecular
components, gases will only reach a small percentage of the colorant molecules while
leaving the others untouched. In addition, the electronic structure of pigments is less vulnerable
to light. The result is that, in general, pigments fade more slowly than dyes.
When it comes to humidity sensitivity, again pigments are usually better. With dyes, the
printed colorant can begin to “redissolve” in high humidity and become “mobile,” the last
thing you want on a print. Pigments don’t dissolve in aqueous vehicles, so they can’t do
this when exposed to high humidity.
But there are downsides to pigments: The larger particles of pigmented inks cause more light
scattering at the surface, which reduces color range or color gamut and makes some colors look
weaker or duller (see Figure 7.3). Rich reds are particularly hard to print with some pigments.
Other pigment problems include:
■ A greater tendency toward metamerism (shifting colors under different types of lights—
see other references in this book). This is a common complaint of the earlier Epson pigmented
printers (such as 2000P) with neutral tones (also skintones) that turned green
under natural daylight. The more recent Epson printers (2200, 4000, 7600, 9600) with
their newer UltraChrome inks, are designed to help reduce this problem.
■ Pigments tend to sit on top of the paper forming irregularities on the surface. In fact,
some—not all—pigments are not recommended for glossy papers since they either do not
dry completely, do not adhere well, or they exhibit what’s called gloss differential or bronzing,
where one part of the image will have a sheen or look duller and obviously different
than another. (One solution to this problem from Epson is found on the R800 printer
that includes not only special High-Gloss pigment inks but also a separate Gloss Optimizer
layer that coats the surface.) The flip side of this problem is that pigments are also not recommended
for use on uncoated, fine-art papers like Somerset Velvet or Arches Cold Press;
Figure 7.3 Although the paper surface
itself also plays a very important role,
the larger particles of pigmented inks
(left) typically create irregular surfaces
and more light scattering, causing
colors to look duller. A print with dye
inks (right) has a smoother surface that
reflects the light back uniformly with
more strength and saturation.
Courtesy of Lyson, Inc.