Paper Color Changes Ink Color
Paper color always influences ink color. A curious and compelling promotional item I received from a popular ink company shows the same solid rectangle of blue ink laid down on about fifteen different colored swatches of paper, ranging from a brown kraft stock to a blue-white offset sheet to a yellow-white offset sheet. You’d think there were fifteen separate shades of blue on those paper swatches even though the actual hue in all cases is the same.
Many—although not all—inks are transparent. Process colors are always transparent. Therefore, when you look at ink on paper, in reality, you are looking at light going through the ink film, reflecting off the paper substrate, and coming back to your eye.
Why should you care?
If you print a photo of faces on a cream-white sheet, the faces can look jaundiced. If, on the other hand, you know this will happen and you choose a cream sheet for a book with mostly text and perhaps some landscape photos, your paper choice will enhance the content of your book.
If you have a dark text sheet (perhaps a gray sheet), and you don’t want the color of the paper to influence the color of the ink (in this case by toning it down—or graying it out—significantly), you might pay the printer more to add a hit of opaque white behind the 4-color photos, to seal the sheet and provide a white background over which to lay the four transparent process inks. This could be expensive, but for a high-profile promotional piece, it might be worthwhile. Depending on the trim size of the job, number of copies, number of inks, etc., the extra cost to add the opaque-white ink behind the photos may exceed several hundred dollars, if not more.
What is Metamerism?
Along with your awareness of the interaction between paper color and ink color, it is also prudent to consider the interaction between ink color and light.
In simplest terms, metamerism refers to the condition whereby two different colors look like the same color under one light source but like two different colors under another light source.
Why should you care?
Perhaps you have specific colors for your company’s logo that you need to match. You can match these with a PMS color, or you can match them with a build of the four process colors: C, M, Y, and K. If you get a sample from your printer to confirm color fidelity, you might be wise to check the colors under all lighting conditions: sunlight, tungsten (regular incandescent room lights), and fluorescent.
In fact, in the controlled setting of a printing plant, press operators check the ink colors on a press sheet under 5000 degree Kelvin light (the same quality/color of light as sunlight). Also, the color viewing booths that printers provide their customers incorporate this light with a neutral grey surround to ensure the color-accuracy of the light. In addition, the pressmen usually have electronic equipment such as color spectrophotometers—as well as their eyes—to check color fidelity.
Another time you might want to check press output under various lighting conditions is when you are trying to match an offset press sheet to a digital press sheet. Keep in mind that this usually will not yield an exact match; nevertheless, you can improve your color analysis by viewing the press sheets under sunlight, tungsten light, and fluorescent light.
Within any print run, you always have three variables: paper color, ink color, and the light under which you view the ink color on the paper color. Trying to control these interactions can be a daunting task. The best way to approach this challenge is to view the ink choices and paper choices under various lighting conditions. In addition, whenever possible, give your print provider actual printed samples showing both the ink and the paper you plan to use. In this way, your printer will understand the final effect you want to achieve.
What is Runnability?
Runnability is actually something your printer may care about more than you do. Runnability refers to the ability of paper to run through the press efficiently and without causing problems. More specifically, ink hold-out (the ability of ink to sit up on a paper’s surface rather than seep into the fibers), dimensional stability (the paper’s ability to maintain its rectangular shape when being pulled through the press), formation (the paper’s physical characteristics, which affect its resistance to having the ink film lift paper fibers off the sheet), and absorbency (the sheet’s ability to absorb ink uniformly) are just some of the elements of runnability.
In short, if your printer says the paper you chose is runnable, that means he’s happy because it won’t cause him headaches and won’t slow down the printing process.
[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.]