Thoughts On Paper
Paper. It’s one of the least appreciated elements of offset printing and yet one of the most important. It’s kind of like a sponge. Too much water in the ink/water balance (needed to keep the ink exclusively in the image areas), and the paper will stretch out of shape. Too much humidity in the printing plant, and its edges will curl. I personally don’t know how printers can keep a flat sheet of printing paper flat, run it through a press, and register (line up) all four process colors of ink correctly. Amazing.
Since process ink colors are transparent, paper also dramatically influences the overall look of a printed piece. It’s a little like painting with watercolors. You see through the transparent layers of color into the paper below. And the lightness (brightness) and tone (whiteness, or color) of the paper affect all the ink laid on top.
Then there’s the texture. You probably don’t think about it. How the paper feels in your hands plays a dramatic role in your reaction to the printed piece. More times than I can count, when my fiancee and I have been looking through art books at the thrift store, she has handed me one and said, "I think you’ll like this.” Almost always it has been a book printed on a dull, bright-white paper stock with a cover that has been coated with a dull film laminate. I’m not even sure she knows this has influenced her.
Qualities of Paper
I’d like to mention a few of the lesser-known qualities, attributes, and things to look for in paper, but I will first briefly review a few paper qualities you may find useful to know:
1. Whiteness: the color of the light a paper reflects. This ranges from a soft, yellow-white, also known as natural, to a brilliant solar white, known as blue-white. It seems to be whiter than white. Bright white paper makes images pop, in contrast to natural white paper, which provides a softer look.
2. Brightness: The amount of light a paper reflects (not the color of light). For instance, a 98 bright sheet in an annual report seems brighter than a 78-84 bright sheet you might use for an automotive catalog. Also, the "number” of a sheet reflects its brightness. That is, a #1 sheet is brighter than a #4 sheet. And a "premium” sheet is even brighter than a #1 sheet. Keep in mind that companies have no absolute determinants of what constitutes a #1, #2, etc., sheet, so compare the brightness numbers instead if you want a more accurate match. Also, check out physical samples (both printed and unprinted). Keep in mind, though, that the chemistry that makes a paper ultra bright usually includes bleach.
3. Opacity. Light-stopping paper. If you’re reading a page of a book, and you can see the text or photo on the other side of the page you’re reading, that’s distracting. An opaque sheet (or, rather, a high level of opacity in a press sheet) minimizes "show-through.”
4. Caliper, weight. Paper is noted as having a certain weight. This is a measure of 500 sheets of a press stock at a pre-agreed-upon "basic size.” Cover paper weight reflects the total weight of 500 sheets cut to 20" x 26", while text paper weight reflects the total weight of 500 sheets cut to 25" x 38". That’s why you can have thick 100# cover stock and much thinner 100# text stock. Go figure (although these do go together well in an annual report: 100# cover and 100# text).
5. Finish: Paper is either coated or uncoated. Run your finger across a page of a trashy novel, and you’ll feel the paper’s rough texture or "tooth." Under a light you’ll see no reflection. In contrast, look at the pages of a coffee-table art book. They are often glossy (which makes images pop), or they will at the very least have a smooth, dull-coated surface (which makes reading easier on the eyes). Sometimes these coated papers are even selectively coated on top of the ink (such as a dull-coated sheet with photos that have been gloss coated with varnish).
Now for the extras that are interesting (and vital to printers) but often not covered in blog posts and books:
Paper comes in sheets and rolls. A web press uses rolls, and it cuts these at a certain point in the process. A sheetfed press uses sheets (maybe 25" x 38"). Maybe you can fit a 16-page press signature for your book (eight 8.5" x 11" pages on each side of the sheet) on a 25" x 38" press sheet (with press marks and bleeds). Once printed (and dry), you can fold and trim this flat press form into a folded signature you can either nest or stack with other printed signatures to create the text block of your book.
But with all of that said, the paper has to stay flat and "true" throughout the process. That means the edges need to be at right angles to one another, and all sheets need to be the correct size. This does not go without saying. Paper may (in an unusual case) be received in an unusable state. Moreover, paper is made up of fibers. They all go in the same way in a press sheet (long or short grain, depending on the direction). But paper expands when the fibers get wet (there’s a lot of water in offset printing), and the paper expands more against the grain than with the grain. What that means is that perfectly good paper from a mill may become dimensionally unstable. This can cause problems with "runnability" (smooth and easy transport of paper through the press) and register (intentionally laying down one color precisely on top of or adjacent to another color). If the paper moves, everything goes wrong.
So you want to maintain the dimensional stability of your paper. That’s one of many reasons printed are highly skilled craftsmen and artisans.
This is somewhat similar to dimensional stability (length and width), only it involves the third dimension (height). Again, remember that paper is like a cellulose sponge. It changes depending on the amount of liquid (water or solvent and especially ambient humidity) in the fibers. So all of this is a moving target.
Paper has to be flat when it goes through a press. It can’t be wavy. It can’t have curled edges. A lot of this depends on the relative humidity and temperature in the pressroom, which is why paper delivered to a printer in the summer or winter, for instance, must be gradually acclimated to the conditions of the pressroom prior to printing. Or there will be problems. Even before inks hits the paper. Just running the sheets through the press will be a headache.
Bulk to Weight Ratio
In addition to the potential confusion between a 100# cover stock and a 100# text stock (due to the different basic sizes at which 500 sheets of paper have been weighed), not all 100# text or cover sheets will have the same thickness. For instance, I used to spec a 55# text sheet for a client’s books that was very rough textured (Sebago Antique 55#). I believe it had a thickness of 360 ppi (pages per inch). A much higher grade of paper another client liked, called Finch Fine 60#, had a PPI of 466 pages per inch.
What this means is that the 55# Sebago was much thicker than the 60# Finch Fine (fewer pages per inch). Both were text sheets (weighed at the same 500 sheets of 25" x 38" stock), but one had been rolled thinner during the paper-making process by the metal calender rollers.
What do we learn from this? Always get paper samples before you ask your printer to go ahead and buy paper for a job. What else do we learn? A smooth paper (even an uncoated one) has often gone through multiple sets of metal rollers in the paper-making process. These rollers have compressed the sheets (made them thinner for the same weight), yielding a smooth, hard paper surface (even on an uncoated sheet). A smooth paper surface allows drying ink to sit up on the surface of the paper and not seep into the paper fibers as much.
In my two clients’ cases, the 55# Sebago would not have been good for 4-color images (which is fine, since their books are text-only literary works, and their readers appreciate the rough paper between their fingers). In contrast, the Finch Fine would have probably been great for 4-color images (although since the paper is uncoated, there still would have been more seepage of ink into the fibers than with a gloss or dull coated press sheet.
So the final thing we learn is that paper choices are relative. Choose the proper paper for the intended result, knowing that heavy ink coverage sits up better on a smooth, flat surface. So ask for not only unprinted paper samples but printed paper samples as well.
[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.]