Opaque White Ink

Process inks are transparent. Light passes through the printed ink film and reflects off the paper. This works well if the substrate is a brilliant white printing sheet. The balanced white of the paper will reflect the light back through the ink and to the reader's eye without changing the hue.

But where does this leave you if you want to print on a muted sheet: kraft paper, for instance?

A client of mine recently chose a kraft paper stock for a booklet and designed the cover art using process inks. Fortunately her goal was to imitate process color printing on a paper bag. Therefore, she was happy that the dirty brown of the substrate would tone down the 4-color art and even change the colors. She did, however, add a fifth color for emphasis. She added opaque white.

Unlike process inks (cyan, magenta, yellow, and black), opaque white is exactly that—opaque. You can't see through it. Which means that the brown of the kraft paper will not be visible through the opaque white, and will therefore not change the color of the ink. Opaque white includes, among other things, titanium white, which is made from titanium dioxide, and which yields a brilliant white base that reflects light back to the reader's eyes evenly without changing its color or brightness.

My client chose to use the white to accent certain portions of the 4-color cover artwork for the book she designed. The white "popped" (stood out dramatically). However, if my client had been interested in having the entire 4-color cover design stand out (that is, had she not wanted to simulate the look of process ink on a paper bag), she could have printed opaque white as a background for the entire book cover image (or most of it).

How would this have worked? Why would it have been a good idea?

For those of you who have painted with oils or acrylics, you probably know that the pre-stretched canvas and canvas boards you buy have been pre-treated with a few layers of acrylic gesso. This mixture of white acrylic paint and other elements provides a flat, evenly coated, opaque surface on which to lay down the oils or acrylics that constitute your painting. It keeps the fine artists' paints on the surface, rather than letting them seep into the fibers of the cotton duck canvas. It's called priming, and it's essentially the same as priming wood before painting it.

Opaque white printers' ink works in much the same way. It provides an even, impermeable ground on which to build the transparent screens of process ink without the image's being affected by the color or texture of the underlying substrate.

That said, there are things to think about before asking your printer to lay down opaque white behind your images. This process requires an extra printing unit, which adds to the cost of the job. If you are already using the fifth or sixth printing unit for varnish or another PMS color, adding opaque white might require an additional pass through the press. This would also add to the cost of the job. In addition, it's easy to contaminate bright white ink (think of how easy it is to soil white clothing). So your printer will need to spend more time than usual cleaning every trace of other ink from the press unit before printing opaque white ink.

Calendered vs. Supercalendered

All paper is calendered to some extent. It is passed between sets of metal rollers during the papermaking process to flatten the paper and provide a smooth surface. The smoother the surface, the more calendering has taken place. The smooth surface allows ink to sit up on top of the sheet rather than seeping down into the paper fibers. This is called "hold-out." It allows the printer to print a hard, round halftone dot that will not bleed or fringe (dot gain). Calendering ensures good holdout.

Supercalendered paper goes one step further. Supercalender rollers are separate from the papermaking machine (Fourdrinier machine), and paper destined for the supercalendered label goes through these rollers as an additional step in the manufacturing process. Wikipedia defines a supercalender as: "a stack of calenders consisting of alternating steel and fiber-covered rolls through which paper is passed to increase its density, smoothness, and gloss."

Supercalendered paper is thin and has a hard, high-gloss surface. It is not a premium sheet. Rather it is a lower grade of paper most useful for magazines, catalogs, and such.

Consider the catalog, for instance. Let's say you have a 300-page book with process color images throughout. It doesn't need to be of perfect quality, but you want it to be light (to minimize postage costs and to make the book thinner rather than thicker in bulk). You want it to be cheap (since paper consumes upwards of 30 percent of the cost of a job with a long press run and a high page count). And you want the ink film to sit up on the surface of the press sheet to allow for the best possible reproduction of the 300-pages of process color imagery.

Supercalendered paper is your answer. Your printer must run this paper on a web press rather than a sheetfed press, but it will save you money and time, and yield an attractive, utilitarian product.

[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.]