CHAPTER 13 HOW PHOTO-QUALITY PRINTERS WORK^197
Dyes Versus
Pigments
1
Dyesdissolve
completely into the
carrier fluid, form-
ing a true solution.
Once dissolved,
the dye should
never separate or
settle out.Pigmentsare
extremely fine, col-
ored powders sus-
pended throughout the
carrier fluid. Because
they’re not dissolved,
pigments have a nat-
ural tendency to settle
out over time. To com-
bat this, the pigment
particles are coated
with a polymer sub-
stance that gener-
ates a static
charge
about
the parti-
cles to keep
them from form-
ing large clumps that
settle to the bottom sooner.Inkjet inks consist of a carrier
fluid, usually deionized water,
that keeps the ink in a liquid state
and is a vehicle for a colorant,
which gives the ink its particular
color. The ink also contains a
drying agent such as isopropyl
alcohol or glycerin that controls the
ink’s drying time. The colorant is
the most distinguishing component
of ink. It can be either a dye or
pigment.The dye dries to
a smoother surface
that is brighter and capable
of a wider gamut of colors. The dyes are, however,
still water soluble, and they easily smear or bleed.
Dye inks also tend to fade unevenly, a failing that is
overcome by applying an overcoating (or special
laminate) that blocks ultraviolet rays, and by storing
or displaying photos away from sunlight and heat.Matched Sets
Printer manufacturers recommend specific papers for their printers. Although the recommendations suspiciously
tend to favor papers they make, this is one time when you should believe them. Inks and papers that have been
created to work well with each other usually do produce richer, more stable photographs than unrelated inks and
papers forced into service with one another.Uncoated paper—the type commonly used with laser printers
and copiers—has an uneven surface that scatters the light, creat-
ing a duller finish. It also has no barrier to prevent the ink carrier
or dye from being absorbed into the paper and spreading out
through porous fibers, which can make the colors look muddy
and the details fuzzy. A high-grade matte finish photo paper also
dulls the photograph but is more resistant to absorption.Paper
Coated paper—covered in a layer of fine varnish or wax—has a smooth
surface on which ink lies more evenly, reflecting light so that ink takes on an
added brilliance. The coating also stops the ink being absorbed into the
paper, which helps to make the image look sharper. Ceramic-coated porous
papers absorb inks quickly, but the ceramic coating leaves dyes exposed to
light and gases, making them more prone to fading and discoloration.
Plastic-coated, swellable paper encapsulates both pigments and dyes when
they seep into the paper’s fibers, helping protect them from light and air.If the colorant is a pigment, the deposit consists of relatively large particles forming
a rough layer of color lying on top of the paper. The thickness of the dried ink
makes it less susceptible to bleeding and wicking on the paper fibers, which gives
fine details an unwanted fuzzy quality.After the ink is deposited on
paper, the carrier and drying
agent evaporate, leaving the
colorant on top of or
absorbed into the paper.2