Printing & Design Tips: December 2004, Issue #41

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.]