Absolutely true. Every color pressman knows this for a fact. There is a very good reason why this is true. And unfortunately, there’s not much anybody can do to change it!
Here is a little known fact outside the printing industry. Full-color printing (commonly referred to as process color) doesn’t print Cyan, Magenta, Yellow, and Black inks as opaque inks. It can’t! If these process colors were opaque, each of the colors would dominate and not mix. Process inks must be remain translucent. Because of this simple fact alone, the black ink used in four-color printing (referred to as halftone black to printers) is also translucent. So what does that matter?
A whole bunch! Since translucent inks are designed to pass other colors beneath (and on top of) them, process black by nature allows the white of the paper color to show through the ink. This means that process black is not technically black in the truest sense of the word, it’s dark gray! When one or more other process colors are printed together, process black appears to be opaque black.
If process inks were opaque, these colors would not blend to give the optical illusion of all other colors. Remember, magenta and yellow create red, cyan and yellow create green, and magenta and cyan create blue, and so on. If these CMY colors were opaque, there would be no red, green, or blue, or millions of other colors created. These opposing colors form the primary basis of color separation- red opposes cyan, green opposes magenta, and blue opposes yellow on the color wheel. When RGB colors are inverted they (pretty much) produce CMY. Black (being not technically a color in RGB mode) is added to the CMY colors for definition and contrast/tonality.
Laser printers use opaque inks but utilize special angles and multiple frequencies (screen sizes) to purposely avoid the deliberate overlapping dots. Inkjet printers print with translucent colors but overcome this problem by adding a second (and sometimes third) shade of black inks to create depth and contrast.
Over the years printing ink rotation (the order in which the inks are applied to the paper) has changed significantly.
When I first started printing process color on a single-color Heidelberg K-series, I laid yellow ink down on the blank sheet first. After a thorough washup, I followed with either cyan or magenta, and last, printed the black. For a single-color pressman running a four-color job, this was a major challenge. Not only was accurate registration of multiple passes through the press a problem, printing the precise amount of each color, and just being able to visibly see the yellow ink at all was difficult. I actually used the light-cancelling effect of (47b) blue Wratten filters (borrowed from the camera department) mounted in an eyeglass frame to enable me to see the yellow ink as it appeared on the white sheet! Who says pressmen can’t be creative? Hm-mm, I got paid way too little.
When today’s presses print process colors, most printers use a different ink rotation, sometimes putting black ink down first. They then overlay the black with the other process colors. With this rotation, if process black were not translucent, any other overprinting colors would not be seen. Therefore- printing projects that include contrast-oriented halftones and not requiring process color should be printed with an opaque black ink commonly known as job black.
This series is a small excerpt from my soon to be released book titled The Digital Image: From Capture to Presentation and Everywhere In-between. If you find this series helpful, think seriously about getting the full book.
That’s the way eye sees it. Feel free to leave a comment and keep the conversation going. If you saw this post listed on a LI group page, add a comment to the listing in that group! Thanks for joining me. If you like this blog, let me know and tell your friends.
If you have an iPad, you can learn more about color and the color separation process from my iBook entitled “The Colors of the Color Wheel.”
See you next time, Herb
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