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Using Black

Click on the headings below to view the information.

Why worry about black ink?

The good news is that if your job is just black, there's almost nothing to worry about. Black can get a little bit more interesting when there are other colors in your job.

Set black to overprint

If you have, for example, black text over a colored background, you should set the type to overprint rather than knock out. In almost every case, the slight shift in the "color" of black caused by mixing the inks is less objectionable than the probability of a slight misregistration.

The image on the right shows an exaggerated and enlarged example of what the two choices are. (Note that it's impossible to accurately show the effect of overprinting inks with the colors in a web-safe palette, but I think this gives you a good idea.)

The word "Knockout" would appear both on the black separation (shown to the left) and as a negative image in the red (shown to the right). In "Knockout," no red ink is supposed to mix with the black. But presses are never absolutely perfect, and it's likely that the hole in the red won't line up with the black absolutely precisely. This results in a white gap on one side and a mix of both inks on the other as shown in the composite image above.

In the "Overprint" example, the word "Overprint" appears on the black separation only; the color is solid. The color will mix with the black, slightly darkening the text and shifting its appearance.

We consider that in almost every situation, it's better to overprint black. Although this example uses spot color for simplicity, it applies to process color, too.

Almost every situation...

There are some exceptions where it's not a good idea to overprint:

• The color shift would be unacceptable. This is pretty rare; most colors are not strong enough to significantly affect black, but this is an aesthetic judgment call.
• You have a nearby black that is on top of another color (or no color). The human eye is pretty willing to consider near-black colors to be truly black. But if you have a black overprinting red and a black overprinting a different color (or just black by itself) nearby, the eye will start to notice the difference.
• The black element crosses between colors (or only partly overlaps the color element). Again, you'll start to see different "colors" of black.

If in any of these situations the black element is fairly large, you might want to trap the color into the black rather than fully overprinting the black.

Rich black

Use support screens to make black more intense in process color

Particularly in four-color process (CMYK), black cannot cover a large area and maintain good density (darkness). Additional inks can be added to the black to increase the density. The simplest way to create this "rich black" is to add 40% cyan ink. We prefer to add a more balanced set of support screens: 60% cyan, 50% magenta, and 50% yellow along with the 100% black. This is still well within the total ink limit and also produces a more neutral tone than when only cyan is added to black.

Don't set type or rules to rich black unless they're very large because of possible misregistration on press.

Use a rich black to match photos

One possible problem to look out for: images and illustrations might not all use the same value for black. This can become visible if the two different blacks cover fairly large areas and are in near proximity to each other. The image to the right shows a simulation of this effect.

Because the photo wasn't tall enough for the layout, a box of solid black was drawn at the top of the page. On screen, most programs will display the two "blacks" as the same shade, but they will print differently. The image to the right simulates the printed effect: there is a noticeable edge where the rich black of the photo meets the box.

(This will be very exaggerated on Macs; I had to boost the brightness of the top black for it to be seen on a PC at all. If you're on a PC and you still can't see the difference on your monitor, try turning up the brightness and make certain you have at least 256 colors displayed in your current video mode.)

To fix this, I would open the image in Photoshop and measure the exact CMYK values of a black area in the photograph (3x3 or 5x5 averaged sample with the eyedropper) near or at the edge that will abut the drawn box. Then I'd define a color in the layout program to match and assign that color to fill the box I'd drawn.

Most photos include significant quantities of CMY in their black areas; many may not even have black at 100%. Also check black values in EPS files such as logos; they're probably set to just 100% black.

Trap items knocked out of rich black.

Another difficulty with using rich black is the temptation to knock type (or other thin elements) out of it. This is shown in the previous example. Not shown is the possible effect of misregistration on press.

Unless the knockout into rich black is trapped (we can do this for you), it is very possible to get little "fringes" of color at the edges of the type. Changing the white to a color that includes some small percentage of at least one of the support plates can help prevent this. For example, if your rich black were defined as C60M50Y50K100, setting the type to C10M10Y0K0 (a light blue) instead of pure white would effectively eliminate the need to trap that element.

To trap knockouts in a rich black, the support screens must be pulled back from the knockout area, leaving just the black to define the edge of the knockout. It will be difficult to see whether this is happening correctly on your laser separations. You might prefer to let us do this trapping for you.