There is no doubt that spot colors can help you achieve striking, effective designs. But spot colors have a dark underside, too; a not-so-obvious behavior that needs to be understood or else it can bite you.
Case in point: The other day, I received an email from a printer who was ranting about a client’s artwork. The client had designed an identity package (letterhead, envelope, and so on) that was beautiful but completely unprintable.
The trouble was with a background pattern built with several overlapping InDesign frames, each filled with a Pantone color or a gradient of that color (see below, though I changed the design and logo to protect the identity of the semi-innocent).
When I say it was unprintable, I mean that while the page would technically print, it would look very different than it appeared in InDesign. This is a case of WYSINWYG (“what you see is not what you get”)!
It’s not entirely InDesign’s fault. Some spot colors are difficult, or even impossible to represent properly on screen. Varnishes and metallic and fluorescent inks are obvious examples of this–there’s no way you’ll get an accurate preview of one of those on a computer screen. Other very bold, rich colors–like bright teals and oranges–are similarly impossible to preview in the RGB gamut of most monitors.
However, in this case, the designer stumbled on a very different limitation of InDesign: the software’s handling of spot colors and transparency effects.
It’s All About Overprint
When you take two process colors (such as magenta or cyan) and overlap them—multiply them, overprint them, whatever you want to call it—the area of overlap gets darker than either of the individual inks. This happens both onscreen and in the printed output.
If you overlap spot colors, some areas get darker and bolder onscreen. But the printed output may be a different situation. Spot colors are more opaque than process colors, and in the case of this particular job, the designer actually overlapped a single spot ink color on itself. The onscreen result was a lovely interaction among the objects. But in the real world, an orange ink overprinting on top of the same orange ink simply cannot result in a darker orange ink:
Unfortunately, InDesign doesn’t usually know that. In the software, when you take two overlapping objects–each filled with the same spot color–and set the top one to the Multiply blend mode, the intersection appears darker.
Note I said InDesign usually doesn’t know that the colors can’t get darker. It does give you a proper preview if–and only if–you turn on the “get smarter about spot colors” switch. That helpful switch ismore formally known as View > Overprint Preview. When you turn on overprint preview, InDesign suddenly wakes up and shows you an accurate preview.
You can see why I recommend that people using spot colors turn this on and leave it on while they work.
Finding a Solution
So what was to be done with this poor designer’s work? The job could not be printed as is. Here are several solutions to remember should you ever find yourself in a similar boat.
First, you could convert the spot color to a process color with InDesign’s Ink Manager. You can open the Ink Manager from the Swatches panel menu:
In this case, the spot color is changed into a combination of process colors (the orange would be simulated with magenta and yellow, and dark areas may even have a little black mixed in). The quality of printing with process colors is different than with spot colors, but at least you’d be closer to the desired end result.
Another option is to use two different spot colors. Combining tints of two different inks can have darker results. (Though it depends on the inks–some thick spot colors don’t tint well, so check with your printer.)
A third idea is to export the artwork as a grayscale JPEG (File > Export), then open the file in Photoshop and convert it to a monotone. To do that, choose Image > Mode > Duotone, then click on the ink swatch and pick the spot color you want to use.
Save the file as a PSD file and place it in InDesign, replacing the original objects. Since this technique leaves you with a rasterized (pixel-based) image, you lose your sharp-edged vectors.
There are other solutions, such as recreating objects in Illustrator, but you’ll still have the same basic limitation: You can’t make an ink any darker than it is, no matter how much of that ink you overlay. If you want some areas to be darker than others, you’ll need to plan accordingly. In the meantime, remember that Overprint Preview is your friend. It’s not a perfect color proof by any means, but it at least brings you to “what you see is close to what you’ll get.”
Read the original article at InDesignSecrets.com: http://indesignsecrets.com/indesigns-onscreen-untruths-overprinting-or-multiplying-spot-colors.php