- Publishing & printing
Ed #9 Understanding Ink
Ed™ knows ink. Where would we be without it? In a much less educated, entertained, and colorful place. Much of what we know about the world begins with a three-micron film of colored liquid. Ink is the lifeblood of writing and printing.
And as printing technology continues to evolve, ink is changing along with it. Today’s inks offer startlingly clear and varied color and an ever-increasing range of special effects, often while being easier than their predecessors on the environment.
So Ed thinks it’s time to take a closer look at inks. Below you’ll see what goes into ink, learn about some of the many types of ink, and gain a better understanding of how to apply it for maximum impact. And while Ed can’t make you an expert overnight, you just might discover something new to bring to your next project.
Why does Ed do it? Because Ed believes in print. And because Ed wants to help graphic arts professionals set even higher standards for creativity and quality.
Ed will never grow old, but some of the information in this issue is out of date.
Understanding ink. Hundreds, if not thousands, of different inks are used today. They all share the same three basic ingredients.
Words are things; and a small drop of ink,
Falling like dew upon a thought, produces
That which makes thousands, perhaps millions, think.
- Lord Byron
It was made of carbon black, lamp oil, and boiled donkey skins. It smelled bad. And it changed the world.
Next to beer, wine, and cooking oil, ink is one of the oldest—and most influential—liquids made by humankind. In fact, the oldest known recipe for ink dates back almost 5,000 years, to the late II Dynasty in Egypt. Carbon black was mixed together with lamp oil that contained a gelatin derived from boiled donkey skins. The gelatin gave the ink its viscosity, along with a strong odor that had to be masked with musk oil. Other early ink recipes called for fruit or vegetable juices, secretions from octopi and squid, and blood from shellfish.
Of course, writing ink is different than printing ink, as Johannes Gutenberg discovered in the mid-1400s. When the inventor of the printing press first tried using it, he found that water-based writing inks were too thin and runny to print clearly. Taking a page from the painters of the day, who were beginning to use oil paints, he replaced the water with linseed oil, and became the creator of printing ink as well as printing.
Today, the basic ingredients of printing ink, as well as the dry toners used in digital printing (see Ed #8), are the same as they were in Gutenberg’s time.
All inks contain colorants—liquid dyes or dry pigments—a vehicle and additives. Dyes and pigments give the ink its color. Vehicles, which can include petroleum or vegetable oils, solvents, or water, carry the pigment. Additives provide the desired performance characteristics. Driers, for example, help the ink dry more quickly. Waxes help the printed surface resist scuffing and reduce setoff, or the transfer of the image from the front of one sheet to the back of another. Other additives allow the pigments to cover more area, protect against drying too quickly, and improve the way the ink bonds with the paper or other substrate.
In virtually all commercial color printing, ink “works” by acting as a filter, similar to a sheet of colored cellophane. Light passes through transparent inks of the three subtractive primary colors—cyan (C), magenta (M) and yellow (Y)—strikes the white paper and is then reflected back to the eye through the colored ink film. Black (identified by the letter K), is added to enhance the depth and extend the tonal range of the colors.
Intermediate colors—colors other than the three subtractive primaries—are formed by laying one film of transparent ink over another. Any white you see is usually not ink, but paper. While there is an opaque white ink, it often requires multiple applications to achieve adequate coverage, so an opaque white foil is sometimes used instead.
Combined in various percentages, CMYK inks can reproduce thousands of hues, but as Ed #5 noted, four-color printing is not full-color printing. It can only reproduce a fraction of the colors that can be distinguished by the human eye. Oranges, greens and purples, intense shades of any color, and metallic tones can be especially difficult to capture using the four process colors.
To correct this drawback, when matching critical colors, the four process colors are sometimes complemented by spot colors, which are applied as a solid and not made from several overlapping screens. In other cases, touchplates print a second hit, or apply an additional screened color, to an image or a portion of an image to increase brightness or reproduce a color that is hard to capture using only four conventional process inks.
On press, ink is dispensed from ink fountains (one for each color) onto a series of rollers. The ink rollers then spread the inks onto the imaged areas of the plate. Meanwhile, other rollers apply water, which repels the oily ink, to the non-imaged areas of the plate in order to keep the ink from covering them. Each plate then transfers the ink to a rubber blanket that in turn transfers the ink to the paper.
To work well, ink must balance a number of often conflicting characteristics. It must be liquid in order to spread evenly across the plates, but it also must dry quickly, to avoid smudging. It must be sticky—or tacky—enough to stay exactly where it is put, but not so sticky that it pulls the coating away from the surface of the paper.
Ink experts use a number of terms to describe the different characteristics of ink, including viscosity, body, opacity, and light fastness or color permanency. An ink’s viscosity, which changes under the heat and pressure of the printing process, is the degree to which the ink resists flowing. “Body” refers to the ink’s overall consistency, which can range from soft and pliable to stiff and rigid. The opacity of the ink is the degree to which it allows the whiteness or color of the stock to be visible to the viewer. Light fastness or color permanency is determined by the chemistry of the ink’s pigments and their ability to resist a shift in color caused by UV radiation or heat.
Hundreds, if not thousands, of different inks are available today. By far, the single largest category, accounting for close to half of all ink sales, are those used in offset printing.
Web offset printing inks are used with high-speed presses that can run at the rate of several thousand feet per minute. To work at those speeds, the inks are formulated with low viscosity and tack. Heat-set web inks contain special solvents that help the ink dry when it passes though the dryer units of the press. Inks used with web newspaper cold-set presses, which typically do not have drying tunnels, are formulated to be absorbed into the fibers of uncoated paper—and to leave ink on your fingers.
Most sheetfed presses use non–heat-set inks that dry by oxidation. The inks typically have a higher tack than web inks to provide good results at slower speeds.
Waterless inks—and waterless printing—eliminate the water or dampening solution that repels ink from the non-image areas of the plate. Instead, a silicone rubber-coated printing plate draws ink to the image area through temperature, which is controlled by chiller rollers on the press.
Several types of ink tackle the environmental issues associated with conventional, petroleum-based inks. As conventional inks dry, alcohol, petroleum evaporate, and volatile organic compounds (VOCs) are released, adding to air pollution. To control VOC emissions, printers must install elaborate ventilation systems. Or they can switch to different ink technologies.
Vegetable-based inks replace petroleum with soy, corn, walnut, linseed, or coconut oils. In addition to practically eliminating emissions of VOCs, vegetable inks allow presses to be cleaned with water-based cleaners, which further reduces VOC emissions and the printed product is easier to de-ink during recycling. Vegetable oils also tend to be clearer than their petroleum-based counterparts, so the color can be brighter.
In the past, vegetable inks had poorer rub resistance than conventional inks, but the difference is not as great as it once was. Drying times have also been improved. Aside from somewhat higher costs, vegetable inks now compare well with petroleum inks, and they even allow for laser printing, foil stamping, UV coating, and other finishing processes.
Ultraviolet, or UV inks, and other energy-cure inks, which are dried by a beam of ultraviolet energy, emit no VOCs. The chemical curing process which the inks undergo incorporates all of their components, so none are released into the air. Because they sit on the top of the paper, UV inks score high in ink holdout, which makes them especially well suited for use with uncoated stocks, as well as with substrates such as glass and plastic films. Applying a white UV ink, followed by process or spot colors, allows you to print on dark stocks in one pass through the press. While UV inks offer a number of advantages, they are roughly twice the cost of conventional inks, and not all printers have the equipment or experience to using them.
Six-color process inks like Pantone Inc.’s Hexachrome® and other “high fidelity” inks expand the gamut of colors produced by conventional four-color printing.
Adding extra colors—which often include fluorescent colors—to CMYK inks captures a wider slice of the spectrum, which allows designers to create special effects and match custom colors. Depending on the two additional colors that are chosen, six-color printing can be especially useful in reproducing oranges, greens and purples.
Six-color printing is not for every project, however. It may not be worthwhile when it comes to blues, which can be reproduced well using the four process colors. There is the time and expense of preparing additional plates, and specialized separating and proofing systems also are required. To gain some of the benefits of six-color without those drawbacks, many printers use highly refined four-color inks, such as Toyo’s Kaleido inks, which offer much of the range of six-color inks, without requiring additional printing units. If six-color inks are used, some experts recommend printing them using stochastic rather than conventional halftone screens.
Used mainly in flexography and gravure printing, water-based inks virtually eliminate ink-derived VOC emissions along with solvent-based cleaners. To use them successfully, however, presses must be calibrated especially carefully, and older presses may not be able to achieve the precision required.
There also is a wide variety of specialty inks.
Metallic inks contain metallic particles such as bronze or aluminum. The metallic particles make the inks opaque rather than transparent, and because the particles cannot be ground as fine as conventional pigments, they can often cause problems on press. Metallic inks require a different ink-water balance than conventional inks, and it may be necessary to apply two hits of the inks to gain the desired coverage. The inks also may need a relatively long time to dry, and the dried ink is often susceptible to rub-off and tarnishing, which can necessitate the use of varnishes or coatings. Unfortunately, coatings will tend to soften the metallic effect.
Available in a wide variety of colors, pearlescent inks create a deep, pearl-like shimmer thanks to special pigments that reflect light at varying angles. The pigments combine titanium dioxide that has been coated with mica and then colored with varying organic pigments. Pearlescent inks are commonly used in car sales brochures.
Fluorescent pigments yield bright colors by absorbing visible or ultraviolet light and emitting it again at a longer wavelength. Fluorescent inks are often used to attract attention in such applications as posters and displays and are sometimes added to CMYK inks to increase the brilliance of the process colors. The inks tend to fade quickly in direct sunlight, however, and two hits of ink are often required to achieve adequate coverage.
Edible inks are not intended as a meal in themselves but used in packaging and wrappers that come into contact with food. They are formulated with ingredients that are proven to be nontoxic.
Thermochromatic inks are heat activated, changing color when they reach a specified temperature.
Photochromatic inks are activated by ultraviolet light, which changes them from a clear varnish to bright color.
Phosphorescent inks glow in the dark after they have been exposed to light. They are often used in road signs, toys and novelties, and safety products.
Scratch-and-sniff ink is made up of tiny capsules of fragrance, each about half a thousandth of an inch in diameter. The fragrance is released when the microcapsules are broken by rubbing or tearing the paper. While scratch-and-sniff inks are used most widely in perfume advertising, the inks are available in a wide range of scents, including cookies and leather.
Scratch-off ink is used in instant lottery tickets and game cards to hide the numbers or symbols that are printed beneath. The information is printed on the card and then covered by a coating that can be scratched off.
While ink and varnish typically account for about 10% or less of a project’s printing budget, they can have a big impact on the finished product. But getting the results you’re looking for can be challenging.
First, it’s important to make sure that everyone is looking at the same colors. That’s where the Pantone Matching System (PMS) and other color matching systems, like the Toyo Ink System, come in. First developed in the 1960s, the Pantone Matching System provides a standard reference for selecting, specifying, matching and controlling ink colors.
Just as preschoolers mix yellow and blue finger paint to create green, the Pantone Matching System uses 14 basic colors to create more than 1,100 solid, or spot, colors. Each is printed on coated or uncoated papers, typically on gloss or matte finishes, along with the formula used to create the color. Printers can order the color by its number or mix it themselves according to the ink mixing formula found in a guide. Another guide compares the solid colors to the closest possible match in standard four-color process printing.
Even with the same swatch, however, you and your client may not see the same shade. Colors can change, or shift, dramatically when viewed under different lighting conditions. Other factors can affect color perception too. Fluorescent inks can fade quickly, so someone looking at an older swatch of the color will see a different shade than someone looking at a newer swatch of the same color. The same is true to a lesser degree for virtually all inks—in fact, Pantone recommends replacing color guides once a year.
It’s also important to remember that the color that’s printed on paper looks different than color on a computer screen. And to complicate matters further, the color shown on one monitor may not match that seen on another.
Printers and others have taken steps to control these variables. Monitors at different locations can be calibrated to produce virtually the same colors. And international color viewing standards, which call for printed color to be viewed in a light booth illuminated to 5,000° Kelvin, assure that everyone literally sees color in the same light.
Of course, there are other considerations as well. The type—and color—of the paper stock can also have major impact on the color. Coated and uncoated papers will yield somewhat different results, which is why each has its own swatchbook of colors.
To see exactly how color looks on the specific stock you’ve specified, you should ask the printer for an ink drawdown. The printer will mix your chosen inks and spread some on the specified stock, either by hand or by using a small press. You won’t be able to see how screens of the color will look, but you will get at least a general idea of the final appearance of the printed piece, which is especially important if you’re using a colored stock.
Inks—and color—are also affected by the shop environment. Heat can cause the tack of the ink to drop, which can cause dot gain. That’s why some people say it is better to print in the morning than in the afternoon. High humidity—and a number of other factors—can cause ghosting, when a faint, shadowy copy of an image appears on the opposite side of the stock on which it is printed.
The key to making ink do what you want it to is to work closely with your printer. Discuss the colors, stocks, and coatings you are considering—and ask about their experience with them. Make sure that all are compatible. Some ink pigments may show undesirable color shifts after an aqueous or UV coating is applied, for example.
Most printing “works” by bouncing light off the surface of paper through colored films of transparent inks. So the brighter the surface, the brighter the color, and the whiter the surface, the wider the range of the colors we see.
The brightness of paper is controlled by how the pulp is bleached, the mixture of dyes and pigments that is used, and often, by the addition of special brightening agents. Higher quality white coated papers have varying brightness ratings, with the numbers reflecting the amount of light striking the surface of the paper that is reflected back to the eye.
While brightness determines the intensity of the colors we see, whiteness determines the range of the colors that we see. A paper that is white comes closest to reproducing the full spectrum of visible light, but many papers have a slight blue tint. That’s because a little bit of blue heightens the perception of brightness and whiteness. The trick is to not overdo it, since the tint can begin to act as a filter and change the colors reflected to the eye.
But there’s more to paper than brightness and whiteness. The surface of the paper is equally important, and the smoother the surface, the crisper the image will be. Rougher surfaces scatter the reflected light, reducing the clarity of the image and distorting the subtleties of its tones.
Ink holdout—the paper’s ability to keep a thin, uniform film of ink on the surface of the paper—is another key factor in capturing color. If the ink is allowed to spread into the paper’s peaks an valleys, the printed dots lose their definition, which results in reduced contrast and uneven density.
So for the best color reproduction, you need a smooth, bright, white surface and outstanding ink holdout. And Billerud papers deliver.
You can find the right kind of paper for practically every project. Gloss allows you to print highly reflective art, such as photography, with wonderful clarity and sharpness of detail. Dull combines lower light reflection with better readability and uniform print smoothness. Glare-free, easy-to-read, matte has a rich, tactile feel that can accentuate high-gloss spot varnishes and coatings.