The Difference between 100% black and four color black text and Why printing registration matters.
The problem with designing artwork with four-color text lies in understanding how a commercial offset press works. Offset presses are equipped with four print heads, each containing a specific color of ink. For example, on a four-color press, the print heads contain Cyan ink, second Magenta ink, the third contains Yellow ink and the last print head contains Black ink.
When we receive your files we need to "rip" those files, which produces four negative color plates; one plate for each color. Our ripping process digitally separates your files into these plates to setup for the offset printing process. Once your plates are on the print heads each with its own color, we then align the plates and begin printing your job. If you have four-color black text in your file, then each color plate will contain a percentage of color to print on paper to reproduce the "black"—which is where the problem lies.
Think about how difficult it can be—especially with smaller type—to send thousands of sheets of paper through 4 print heads while keeping every plate aligned in perfect registration for each letter in every word. If only the black plate contained the color information to print your text, then there is no problem because the text printing is actually being produced from one plate and not a combination of four.
So, Best Practice? Black should only be Black.
The idea here is that, when a given color should be printed Black, its color formula should be 100% black, with all other colors set to 0%. Note that this does not apply to Rich Black; which we will discuss in a later post. We'll go over this example in Adobe InDesign, but this practice applies to all other design programs that allow for color separation (eg. Quark, Illustrator, etc).
The Wrong Way:
Here we are setting all 4 colors to 100%; which, on screen, gives us a color of Black. However, this is going to cause two problems: 1.) the dramatic waste of ink, and 2.) the registration troubles we discussed above.
The RIGHT Way:
Here we are setting Black (K) to 100%, and all other colors (Cyan [C], Magenta [M] and Yellow [Y]) to 0%, which doesn't waste ink, and since we are not going to experience those registration problems, is going to give you a much sharper appearance on small/thin text and fine line treatments.