Spot color printing is a method of printing that only lays down one color of ink at a time and does so using solid fields of color. The color of the ink on the press is the color of the ink on the final printed piece. Any adjustment to that color is made by directly adjusting the ink mix or increasing/decreasing the amount of ink on the press.
In contrast, the majority of printed materials are produced via four-color-process or “process” printing (think: desktop printer to the massive printing presses that spit out the Sunday newspaper). This is often referred to as CMYK due to the four colors used: cyan, magenta, yellow, and black (black is referred to as “key” in CMYK printing because the other three colors are carefully aligned/registered according to the placement of the black plate). These four base or “process” colors are used to portray the full range of color via optical mixing. In pre-press, a photograph is split into halftones of each of the four channels of color and on press each of the process colors is printed in a dot-pattern. The size and proximity of the dots of all four colors together allows the viewer’s eye to do the rest in order to perceive a full range of color. If you magnify the images in a newspaper you’ll be able to see the actual dots of ink on the paper.
Spot color printing offers the most solid ink coverage and the most accurate color match to specified colors. However, running each color one at a time is more labor intensive and can get pricey quick. Each color, unless it is a pure Pantone process or base color, must be mixed according to specifications. Each surface that a specific color is printed on for a specific job—whether it’s multiple pieces or multiple sides—requires its own printing plate and its own press setup. Simply put, the expense of multi-color jobs is the biggest reason that most letterpress jobs don’t often go beyond two or three colors at most, but that’s not to say that they never do.
At Smudge Ink, we use the Pantone Matching System (PMS) formula guide for uncoated papers. The PMS system allows for the consistent matching of colors across a variety of printing methods and surfaces. When a client asks for “burnt-orange” or “Carolina blue” that can be a very subjective thing. On the other hand, Pantone’s system contains 1,867 colors and their specific formulas for mixing. This allows client, designer, and printer to all communicate very clearly about the desired color(s) for a project which is why we request that all of our clients refer to PMS swatches when specifying colors.
The Pantone Formula Guide is a worthwhile investment for every designer and their Color Bridge provides a visual comparison of spot colors and their closest CMYK process printing match. If you need the Pantone guide infrequently enough to justify the expense of buying your own, and you are not close enough to visit us in person, Pantone does offer a Starter Guide for $60 or you could check with your local FedEx/Kinkos to see if they have a guide you could reference.
Thanks to Pantone, if a client specifies "PMS 374 U" in their project brief, I know to find the formula for Pantone color number 374 for an uncoated stock. There is a separate formula (374 C) for mixing that same color to be printed on a coated stock, but we typically only print on uncoated papers. The swatch for Pantone 374 U lists the mixing formula in percentages so that depending on the amount of mixed ink I want, I know how much of each base color to use. Older Pantone books also list the formulas broken down into “parts.”
Of course, because our inks use a transparent base the final printed color does mix optically with the color of the paper. In addition to that, uncoated papers tend to absorb the ink like a sponge which often leads to a salt and pepper or “mottled” appearance. Both of these things must be considered in the process of mixing and printing the inks, but we will address these issues in future posts.
Do you have any letterpress-related questions for George? Please email him at info[AT]smudgeink.com!