Guest Post by John Prothero, Printing Specialist
“It’s just ink on paper” is a common phrase in the print industry. And truthfully, it is. But more than that, printing is a craft, requiring great skill and knowledge on the part of press operators to achieve the results that the client seeks on the final press sheet. In this blog we’ll cover the basics, to give you as the client an understanding of how the process works.
Granted, it’s drastically changed in the last few decades, but the science and art are the same.
First off, we print in the CMYK world, which means our presses print in cyan, magenta, yellow and black. This really hasn’t changed, and I doubt it ever will. Often you print in what are called PMS colors, which means Pantone® Matching System, the international standard for colors that you can print with. Most print shops will have at least a 4-color press, many have a 5-color press (which can allow printing in a 5th or “spot” color). Many presses have capabilities for running 6-colors, which can allow for PMS colors, or inline varnishes. Each “unit” of the press (the tower that holds the ink, the printing plate, the impression blanket and impression cylinder, and all the rollers) is dedicated to specific colors. So, you might have the 1st unit running black, the 2nd unit running magenta, the 3rd unit running cyan, and the 4th unit running yellow. There might be a 5th unit running a client’s corporate color. And some shops run their color in different sequences, since they may have different ink manufacturers or different presses.
The science behind the process is this: oil and water don’t mix. Now, most inks today are not oil based, but soy based, and the chemistry in the presses is different too, allowing for the same principle of oil vs. water to work in a synthetic environment. The ink is loaded into ink fountains (they look like trays) at the top of each tower and distributed by several rollers to the printing plate. The printing plate, which is a photosensitive sheet of aluminum, has been laser etched and processed through a solution that removes all the non-imaged area. Those image areas are receptive to the ink. In addition, there is a solution that lightly coats the plate so that the ink stays ONLY on the imaged areas. The ink is transferred to what is called a blanket, which is a flat sheet of rubber that is placed onto the blanket cylinder. The blanket often has behind it sheets of paper of varying thicknesses to ensure the plate and the blanket press against each other to transfer the image onto the blanket. This is called packing. The blanket transfers the ink to the press sheet, and as it passes under each tower, each color is applied to the sheet until it has printed all four colors. The art of all this is knowing how much packing to put in, how much ink to use, the pressure of the various cylinders, the balance of the solutions you have to use – and determine that for EACH printing unit!
To further emphasize how much this is an art, the press operator’s skill comes into play when he or she sees the color on the sheet, and determines how much to add, or how much to take away from one or more colors. The subtle balance of adding 5 points of magenta, or removing 3 points of cyan, and doing it in specific areas on the sheet, truly is a skill. Press operators use a device called a densitometer, which reads small boxes of each color on the sheet, and tells them the density of the ink that is being applied to the sheet. The press operator can then reduce or increase the ink to a specific area of the sheet to affect the color in a specific area. When you take all this into account, and then add the press operator’s knowledge of the paper that the job is running on, or how to adjust the packing and ink balance for that specific paper, and you can easily appreciate the craft.
About the Author
John Prothero, Business Development Coordinator, Westamerica Graphics, Foothill Ranch, CA
John Prothero is a 30-year employee of Westamerica Graphics, a commercial printer based in Orange County, California. In his 30 years at Westamerica, John has done delivery, bindery, proofing, plating, traditional prepress (stripping), scheduling, job planning, job management, account management, and digital job production. Currently he is the Business Development Coordinator, working with the marketing team in creating blogs, social media posts, and tools for the company’s sales team to enhance and grow the company’s sales.
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