What is Paper Coating Made Of?
Coating -- or the lack of coating -- can
dramatically
affect the appearance of the final printed piece.
But what exactly is coating? Coating
is a mixture of clay, white pigment, and binder. It comes
in three degrees of smoothness and hardness: dull, matte,
and gloss coating. When applied to a printing sheet, coating
provides a surface on which ink can sit (called "hold-out"),
in contrast to the uncoated surface of an offset or opaque
sheet into which ink is absorbed. The hardness
of the coating--gloss being the hardest--minimizes dot gain,
in contrast to the softness of an uncoated surface such
as an offset or opaque sheet. Type and halftone dots do
not spread as much on coated stock and therefore have crisper
edges. Photographs seem
sharper, and colors appear more vibrant and consistent.
Surface coatings not only provide a
certain look but also affect readability. The smooth, hard
surface of coated paper reflects light more evenly. That
is why a gloss coating really makes photos jump off the
page. However, the glare of light reflected back to the
reader can tire the eyes. A dull sheet, on the other hand,
makes photos a little softer in appearance but at the same
time improves readability. Consider the matte sheet -- which
is a little less smooth than a dull sheet because the coating
is not as uniform, and is
cheaper to produce -- as another good choice for text-heavy
documents.
What is the Difference Between Whiteness and Brightness
of Paper?
These terms are not interchangeable.
Brightness refers to the amount of light reflected back
to the reader's eye. A bright sheet makes photos "pop"
due to the contrast between the paper and the ink. An interesting
and useful fact is that the paper
grades -- premium, #1, #2, #3, #4, and #5 -- are distinguished
one from the other based on brightness. Bleaching the paper
to increase its brightness moves a printing sheet up the
scale to a smaller number and increases its price.
Whiteness, on the other hand, refers
to the quality (as opposed to the amount) of light. A white
sheet evenly reflects all colors of the visible spectrum.
However, papers inherently have either a warm,
yellowish tinge or a cool, bluish tinge. In general, blue-white
sheets appear brighter than comparable yellow-white sheets
(although this is not always true once ink or varnish is
applied).
If blues and blacks predominate in
your design, a cool white sheet (blue-white) will make the
colors appear brighter. If reds, yellows, and oranges predominate,
these colors will appear clearer and more vibrant on a warm
(yellow-white) sheet.
What are Bleeds and Why Do Bleeds Cost More?
A bleed is created when an image area
extends past the trim. After your job has been printed on
a sheet larger than the final size of the piece, the extra
paper is cut away, giving the impression that the
image exceeds the bounds of the page.
When you bid out your job to an offset
print provider, mention that your job includes bleeds. This
will affect your final price since a job with bleeds must
be printed on a larger sheet than a job without bleeds.
If your job will include bleeds and
you will need to print on a larger sheet, this sheet may
no longer fit on the press that would be appropriate for
a non-bleed job. If so, you will have to pay a higher rate
per hour for the larger press. In some cases, however, slightly
reducing the final trim size may allow you to use the same-size
sheet you would have used for the non-bleed version and
the same size press as well. To be safe, discuss press size,
sheet size, and the optimal size of the printed piece with
your printer early in the process.
Halftone Dot Shapes
Halftone dots come in many shapes,
not just the round ones you might expect. Common alternative
shapes include square, diamond, and elliptical.
Dot shape has the greatest impact on
midtones, where the growing dot area causes corners of the
dots to connect. When adjoining dots connect, they bleed
together causing "dot gain." When dots expand
from minimal coverage to 50 percent coverage to maximum
coverage, a tonal shift occurs, in which midtones jump from
being too light to overly dark.
Creating halftones with alternative-shaped
dots such as elliptical dots (which are initially connected
to one another only along one axis) may minimize tonal shift,
allowing for smoother gradations and improved flesh tones,
for example.
Unfortunately, elliptical dots are
more prone to causing undesirable moiré patterns.
There is a bit of a trade-off, with round dots maximizing
dot gain and minimizing moiré and with elliptical
dots doing the opposite. Square dots present a similar problem.
They allow for sharp detail in midtones but are also less
resistant to moiré patterns. The challenge is in
finding the right balance. And although you can manipulate
dot shape from within such page composition software as
Quark or PageMaker, it is prudent to discuss this with your
printer first.
[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]