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Prepress & Screen Making



We’ve all had the client from hell who can’t seem to approve anything we send them without a fight or an outright rejection. One client of mine, who was unbelievably critical, immediately comes mind. We could never get our color matches right. Our solution was to do our best to color-match an ink color and then cut it into three different parts. Being careful to disguise the color’s source, we’d send the color-sample chips with a note saying one was more red, one more yellow, and the middle one was our best choice.

Invariably, the client would pick one of the two that we didn’t select and would send some sarcastic note informing us of our incompetence with color. It was always good for a chuckle. However, like most issues in our industry, the closer you look at a situation, the less likely you are to find the obvious. That’s exactly what happened with these color approvals. This scenario demonstrates that the ability to maintain reliability and continuity when viewing and evaluating images is critical, whether you’re in the pressroom or at the client’s location.

While this month’s column is not limited to the prepress portion of the production process, it directly relates to the immense complexities of getting a client to approve images and color. What follows is an overview of the key areas you need to study and understand when it comes to getting client approvals.


Viewing images and color

We determine how we’ll view images and color for approval at the very front of the process. We can view under two conditions: emissive and reflective. Emissive refers to our computer monitors and is how we see all of our images before they’re converted to reflective versions on press. Each has its own set of control points and characteristics. Our goal is to minimize the differences between the two to the point where there are no appreciable variations. This is the holy grail of proofing, and most color experts would agree that we’ve finally achieved the objective.

As a foundational baseline, let’s summarize the variables for each viewing perspective. Viewing color temperature is D65 (6500° Kelvin) in emissive conditions. Now we must consider the differences between LCD and CRT monitors. The former is notably more stable over time than the CRT monitors of old. The type of calibration software we use (see “Digital Remote Soft Proofing: The Key to Effective Color Communication,” June 2008, p. 30, for a list of popular applications), surrounding neutral color, white point, and black point are all critical. It’s also important to make sure the ICC profile created by the cali-bration software is loaded on your machine and translates to the design applications in use.

The conditions for reflective viewing are different. The color temperature has been set to D50 because each of the energy levels of the R, G, and B colors at that color temperature is equal, resulting in an equal spectral distribution of color. This supposedly delivers a neutral white without any visible color cast. You must also know your luminance level. The ISO specification (ISO 3664-2000) sets it at 2000 lux ±500 lux. The neutral gray surround also is specified.

Light-source variation is a limitation of the D50 standard. For one thing, it’s almost impossible to get an exact 5000°K fluorescent source. The phosphors change over time, and the spectral output is missing some frequencies. Most professional viewing booths have hour meters that indicate when to change the bulbs. The best alternative is to use calibrated instrumentation to measure the color temperature and luminance on a regular basis.

The reason I’m going to this length to describe the viewing conditions is so you can communicate more effectively with your clients. When they’re making decisions, and their conditions do not match yours, there’s no way to achieve any reasonable match. The same color viewed under two different light levels and color temperatures may very well be completely different. A perfect match under one set of lighting may be completely rejected when viewed under another set. The effect of color changes under different lighting conditions is known as metamerism, and the suspect pigments are called metameric colors. Fluorescent color is an excellent example.


Use of image and color

Let’s consider how the image or color will actually be used. If you’re doing retail P-O-P display work, it’s best to match under the actual usage conditions. Retail lighting is considerably warmer than what we find in graphic-arts-proofing standards. Likewise, it’s best to ask your client before you start production which conditions they would choose as the basis for color evaluation. Such a proactive approach can greatly improve the communication between the two of you.

Now that we’ve established viewing conditions, let’s spend some time on the Pantone Matching System and some of the variables that affect how we achieve a match. At the very front of the process is the Pantone book itself. If it’s more than a year old, I would be very suspicious of any of the colors. I’m amazed at how ratty the books are that end up in the production areas and ink-mixing rooms. As an owner, I am hesitant to buy new books every year at almost $100 each for everyone who needs to specify color—particularly in the ink lab, where careless technicians mishandle the books and render them useless.

Pantone books can vary widely from year to year. I distinctly remember a new batch of books that varied from the previous by as much as 15 Delta E. Because printers generally strive for a 2-3 Delta E variance in achieving a color match, 15 is clearly unacceptable. The problem came when Pantone changed their ink base and paper. The values were so far off that I called my spectrophotometer manufacturer to make sure my instrument wasn’t out of calibration.

Are you matching coated, uncoated, or matte values? Pantone is based on lithographic printing. Screen inks have vastly different surface-reflectance values. Since we deposit six to 20 times or more ink than what’s used in litho, our final result won’t look anything like the litho ink on paper.

Our substrates are quite different as well. Not only do we often have se-vere color casts to contend with, but there also are often significant texture differences. A perfectly smooth, coated offset sheet is an ideal surface to match against. Unfortunately, our surfaces rarely match the surface on which the books are printed.

The mesh count, tension, off-contact, squeegee durometer, and squeegee pressure all have a bearing on what color looks like. If you use a wire-wound drawdown as your control, the final printed piece will vary in direct proportion to the ink deposit’s thickness. An ink film thicker than the control will color shift to the blue shade. Thinner deposits than the control will color shift to the yellow shade.

More pigment particles reside in the thicker ink film. Light hitting the film is absorbed and reflected back. The thicker layer scatters more of the longer wavelengths of light, resulting in more blue and violet frequencies returning to the viewer. That’s why we detect shifts to the blue side from the control. Think of a swimming pool viewed from above. The shallow end is aqua (more yellow) and the deep end is darker and bluer. The color changes continuously from the shallow end to the deep end. The same is true with our ink film. Some colors are extremely sensitive to this, such as neutral grays, tan, beige, light blues, and pinks. Generally, the lighter the color, the more pronounced the shift in color.

When delivering a color match, I almost always ask for a physical chip of the color I’m being asked to match so I can have a known target to which I can adjust. The formulas in the Pantone book are a starting point only. There are simply too many physical variables for us to stick to just the formulas.

Lastly, when submitting your color sample, go back to what I mentioned earlier about submitting three different samples. While the example I shared was in jest, you have a very real obligation to provide matches that define the tolerance of color change that occurs during your run.

Printed color constantly changes. As temperature changes during the day, mesh tension drops, and your squeegee becomes dull. Today’s mo-dern color-measurement instrumentation is relatively inexpensive and very accurate. With only moderate effort you can quickly determine how each of these variables works, and how you can make them work in concert to cancel each other. Measurement is the key. Without it, approved color becomes a very small bullseye that is very difficult to hit and maintain. Using the Delta E measurement function you can establish a defi-nitive value that you can set in advance. Your client will then have an additional layer of confidence knowing you are monitoring and adjusting machine drift as it occurs.


Color commentary

Color matching and approval can be as much science as it is witchcraft. It’s been the bane of many a printer over the years. Color is always subjective, even when we have precise instrumentation. There are three main ways for dealing with color rendering. They are perceptive, relative, and colorimetric. The same color looks different when viewed under each of these parameters.

Color viewing and matching are complex processes. Education and communication will help you solve problems associated with these tasks. The most successful collaborative relationships are those in which the printer works to educate clients and understand their objectives. Most clients are ignorant of the significant technical variables that affect how their finished work will look. It’s our job to lay a solid foundation upon which we can deliver consistent, predictable, and repeatable results that meet or exceed our clients’ expectations.


Mark A. Coudray is president of Coudray Graphic Technologies, San Luis Obispo, CA. He has served as a director of the Specialty Graphic Imaging Association Int’l (SGIA) and as chairman of the Academy of Screen Printing Technology. Coudray has authored more than 250 papers and articles over the last 20 years, and he received the SGIA’s Swormstedt Award in 1992 and 1994. He can be reached via e-mail at



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