Color Management for Screen Printing
Removing variables in evaluating and controlling color is critical to quality on press.
Color management can be a challenge for screen printers, because the media that we print is constantly changing. A printer may have different shirt colors, different fabrics, strange garments, and a huge variety of art sources that are provided to color match.
Before the actual inks on the press can be matched to the art sources from a customer, a few steps can be taken to ensure that colors can be properly dealt with and that time won’t be wasted by making assumptions prior to the actual method of ink-to-screen matching.
It is always a good practice to first review a color to see how different the actual creation of color is depending upon the way light is displayed. Once the methods of color creation are understood from each visual display of a specific color, then the best and fastest method of color reproduction can be determined. Follow the path of the color as it is displayed in each of the three areas: from the first preview in a manual or digital sample, after it is duplicated or edited and then sent back out as an art proof, and finally as a production proof and on-press ink sample.
A quick look at the properties of color and how they work with the different displays common in a screen-printing shop will help to illustrate the challenges that can crop up in the day-to-day color-managing process. First, the most common components of color itself are hue, saturation, and value.
Hue This quality in color is the specific wavelength of light that is reflected and, therefore, creates the color. If a color shows as Royal Blue, then what that means is that all of the other colors in the wavelength of light are absorbed into the surface and only the blue is reflected (Figure 1).
Saturation The saturation of a color is how much pigment of a color is presented in the base that supports the color (Figure 2). One way to think of this is if you have a gallon of clear water and ten blue golf balls floating in it, then that gallon would have a relatively low saturation of blue, and the color would look like a lighter blue. If that same gallon then were to have 40 blue golf balls in it for a higher pigment-to-base ratio, the saturation would also be considered high—and then the color would look more like an intense blue.
Value The value of a color relates to how much white or black is mixed into the color, effectively darkening or lightening the color (Figure 3). The difficult issue with value—or brightness, as it is sometimes called—is that it can dramatically affect the hue of a color while still not changing it. A bright green hue, for instance, may appear as a grass green, a mint green, or a forest green depending upon the value of the color and how much white or black is blended into it.
Another consideration that can be important is that the typical gamut range, or the amount of colors that are included in a specific color system, is larger on a monitor that creates colors using RGB color space than a color-gamut range in print that can be created by blending inks together. What this means is that careful reviews must be made in regards to artwork that was created on the computer with very deep, saturated tones, because they may be very difficult to replicate in the screen-printing process.
Reviewing the art inbox and color management
The first step in standardizing color management in the art department is to take an outside-in look at how artwork comes to the department and how it is reviewed. Artwork will commonly come into an art department in two ways: a physical sample/reference or as a digital file. The easiest way to manage both of these types artwork and the colors contained inside of them is to look at the environment that surrounds them. All color is created by reflected light, so the environment that surrounds the area for viewing colors is very important.
Reviewing physical samples or artwork When art is brought in on a paper reference or on a previously printed shirt, it should be viewed in natural daylight or a daylight light source that is brightly lit without any large areas of color pollution. Color pollution will happen, for instance, when a room is painted a specific hue. All light in the room will be adjusted to that hue prior to viewing a sample. If your shop is painted a funky color, then it is a good idea to create a light box for viewing art samples. This is a simple box with semi-transparent walls that is lit with diffused daylight light sources so color can be viewed, compared to Pantone swatches, and recorded for art reproduction.
Viewing digital samples of artwork The most popular method of art review is obviously using a digital file on the computer. Unfortunately, every computer monitor, video card, and room environment will change the colors on the screen to a degree, so it can be a challenge to accurately view colors. Never assume that you see the same colors as the client does on their screens, phones, or tablets. The best you can do is to handle the viewing area that the monitor is in using the same process as a physical sample to start. Make sure the monitor is in a properly lit area that has a natural daylight light source. Observe the area to make sure it’s free of strong color reflection from surrounding walls or posters, etc.
The next step is to look at the computer monitor itself. Advances in monitor technology have come a long way, but there is a strong tendency for modern, flatscreen monitors to be too bright and their contrast set too high. Here, the deepest shadows and subtle changes in the dark areas will turn completely black and disappear. The light grays and pastel colors will tend to appear like white on a high-contrast setting, so it is important to test your monitor with some color references and make sure the lights and darks are accurate.
A quick way to check your monitor for value and contrast settings is to get a color reference (many art Websites and programs will provide these references), turn down the brightness until the monitor is very dark, and then slowly increase the brightness and watch the value graduations carefully to make sure you reach the point where the monitor is visually accurate but not too bright. The next step is to do the same with the contrast and adjust it by tuning it to the best level (Figure 4). Several companies also offer monitor-calibration units that will adjust a monitor to match a color working space. This is a typical step for offset printing but not as common a practice for screen printers due to the lack of standardization in the screen printing-inks.
Once the monitor is properly adjusted, you can then address the software that will be used to view the images and then recreate or separate the artwork. Adobe software provides some elements that can be used to help a screen printer to work in the right color space and aid in viewing proofs and final, recreated logos in Photoshop or Illustrator.
Color consistency from the monitor to customer proofs
The color that you see on a monitor is different from the color that is reflected on a piece of paper. The way a monitor creates color is by combining wavelengths of light from the RGB spectrum (similar to the way our eyes recreate light). On paper we try to emulate that reflection by merging ink colors from the CMYK spectrum of inks. Even a properly calibrated monitor will not perfectly match a print out because the way the colors are created is different.
There are detailed systems in use to calibrate monitors for offset printing and proofing. Screen printing typically involves less consistent print surfaces, so an offset calibration will not carry over to screen inks. Additionally, the separations that work properly for printing on an offset press will not work well for a screen-printed surface. Ink formulas, dot gain, and other variables are too dissimilar.
The easiest way to adjust your monitor is to use a visual reference, making sure the subtle shadows and highlights are recognizable and don’t show an incorrect color cast. Also go through all of the computers in use in your company and compare a color reference to all of them to ensure that they all display the proper detail and hue qualities. It is very common for the computers in sales to be tuned different from those in the art department—and then, even the various computers inside the art department may display a wide variety of values and contrasts using the same image if they are not adjusted all together.
Of course, you can’t control customers’ computers on the other end of the viewing process, so it is a good idea to standardize your proof output if you send customers digital files to review. A couple of tips for this include:
1. Convert all files for customer review to RGB so the images can easily be viewed on monitors, phones, and on computers using a variety of software applications. Be careful about sending reduced-gamut CMYK files, spot colors, or other multi-channel color files because they may cause dramatic color shifts on the customer side.
2. Reduce the size of all images to be sent in e-mail or through a Web-based application. Excessive file size may cause color or display problems, and large files may be rejected by e-mail servers or firewalls.
3. Always ask clients to review a basic, Web-based color chart, or send new clients a color chart that is properly calibrated for your monitors and standard inkset. This way, you can use this reference in case the client has an improperly adjusted display and insist they compare the proof to colors from this reference in case of a client-side color question.
4. Include a small disclaimer on the bottom of color proofs to clarify that colors may vary slightly from what is shown due to the nature of the screen-printed garment. Pantone simulations that are created with screen-printing inks may vary slightly from those created using offset inks. If you feel this may scare customers, you can just post it on the color reference or address it when it comes up, but it is always better to be prepared when a client wants an exact color match to a printed piece or collateral.
From monitors to garments
It is a simple matter to match a color from a monitor or print to a screen-printing ink by using any of the color-mixing systems from popular manufacturers of screen-printing inks, as long as the color calibration front end is properly done. It is also a good idea to check with your local screen-printing supplier from time to time to see if any new matching systems have come out.
Many computer manufacturers have different methods of calibrating a monitor, depending on your environment. If you need controls that are more strict than what’s common in garment printing (as in high-detail flat-stock or decal printing), it is a good idea to research different ink companies to find the latest solutions. A little background work in color calibration will save you some serious dollars by helping you avoid costly mistakes.
Thomas Trimingham has worked in screen printing for more than 21 years as an industry consultant, freelance artist, and high-end separator. He is an award-winning illustrator, designer, and author of more than 110 articles on screen-printing art and separations. For more information, contact him through his Website, www.screenprintingartist.com.