The Usage of Black
As the most combustible rock band of all time so eloquently pondered, “How much more black could this be? And, the answer is none, none more black.” There comes a point when doing more is, well, pointless.
Not all design is created equal. A graphic that is designed for web may not necessarily be suited for print. Graphics for web are usually intended for an RGB color space as produced on a monitor, where color is created using emissive light. Graphics for print are usually intended for a CMYK color space as produced by 4-color process, where color is seen with reflective light. Although the end result of the graphic may be visually similar, the way that the colors are built can be vastly different, particularly with dark colors.
When designing for web one may take into consideration the resolution, video support, transparency, scaling adaptation, and device differences. Color builds or limitations are not really a factor because the RGB color space is very large. Although the human eye can see more colors, L*a*b* and RGB gamuts are the largest that can be produced by most media devices. Though there are limitations in what an emissive light device can produce due to its resolution and components, there are virtually no limitations in what an emissive light device (monitor, TV, etc.) can “attempt” to produce. Therefore, there is no real concern of whether a color is too vibrant or too saturated. The monitor will produce that color to best of its ability. There is some consideration for consistency, however. When it comes to branding, given the fact that the same color can be reproduced many different ways depending on the media, designers should take into account color conversions when choosing brand colors. To help manage the consistency of a brand across multiple channels, designers should consider colors that convert from Pantone® solid colors to CMYK and RGB well; and be diligent in using the proper HEX, spot colors, or CMYK builds when designing for different applications.
When designing for print, one must still consider the resolution and media application, but also how the colors are going to be reproduced. Printing involves physical components–ink or toner being applied to a media surface like paper or plastic. In lithographic printing this is typically ink on paper. Each of these components has its limitations and tolerances when it comes to their contribution to the end result–that being the finished printed product, and in particular, the color. Ink has limitations in its pigments and density (how much ink that is applied to the paper). Most full-color printed media is printed using CMYK process. A CMYK process ink set consists of cyan, magenta, yellow, and black. These four colors are combined in different percentages to create all the colors we see on printed products. For instance, yellow and magenta make red, cyan and yellow make green, etc. Some printing devices use other colors in addition to CMYK such as orange, green, and violet to produce an extended gamut, but at the core of full-color reproduction, and what most printing devices and large presses use, is just the primary four process colors.
The four process colors are combined in percentage and measured in whole by total ink limit. With each color in the 4-color process at 100% the total ink limit is 400%. This is the maximum ink limit that can be produced in CMYK process. However, actually printing 400% ink coverage is usually a problem. That is more ink than most paper can absorb. Most offset presses typically have a max ink limit of around 300%. If the amount of ink on the sheet is much more than that it starts to cause issues like setoff. Setoff is where the uncured ink transfers to the back of the sheet on top of it as it sets in a stack. In a UV press, where the ink is cured with a UV lamp, too much ink can cause it not to cure completely. Most print shops will run an ink limit of around 260% to avoid any problems with setoff or curing. Even a 260% ink build can cause problems depending on the total ink coverage on the sheet and other factors such as water/dampening settings, ink manufacturer, and paper type.
Generally, a 280% ink build or more is black, though there can be some dark green, burgundy or brown colors that are more than 280% ink. These dark colors are typically adjusted to a lower total ink percentage in prepress through the use of GCR (gray component replacement). GCR is part of a color profile that takes the shadows created with cyan, magenta, and yellow and replaces them with black. Where a dark brown color may be originally built as C70 M100 Y90 K40 (300% total ink), GCR would convert it to something like C20 M75 Y60 K80 (235% total ink). This allows virtually the same color to be reproduced with less ink.
When it comes to black there is usually a point where adding more ink does not necessarily make it darker. Adding varying percentages of CMY to 100% black ink can create different hues of rich black, but at around 260% total ink, any additional ink just creates saturation without adding any depth to the color. We recommend a mix of C35 M25 Y25 K100 for a rich black build. This produces a dark black at 185% total ink with a neutral hue in the gradients and tints.
Most of the time it is preferred to run only 100% black ink in graphics and text unless there are large areas of coverage where a rich black build would help with richness and consistency. This is especially true with small text. All small text that is black, close to black, or gray, should be created with only black ink. This is recommended primarily to ensure sharpness in small text. If small text or graphics are created with a rich black build there is the risk of visible registration issues. This occurs when all four process colors are not exactly in register with each other. This can cause the text to look thick or blurry. Colors being out of register on at least some areas of the sheet can stem from several minute things in the print production process, such as paper stretch, and is not always avoidable.
Text unknowingly or unintentionally being assigned to rich black or registration color is probably the most common issue we see in prepress. Most prepress workflow systems can automatically recognize registration color and change it to 100% black. They can also usually give a warning if any small text is colored with rich black, but these systems are not foolproof. Transparencies, outlines, or other factors can cause problematic ink builds to slip through automated preflight systems. It is highly recommended that the black channel be checked using separations/output preview in Adobe programs prior to sending file to the printer. This check can be performed by turning off the black channel in separations/output preview and analyzing all pages of the document. If any small text or unusually dark gray graphics are visible then that indicates small text is assigned to a 4-color build or graphics are assigned to a higher total ink build than recommended. Separations/output preview can be found in InDesign under Window>Output>Separations Preview, in Acrobat under Tools>Print Production>Output Preview, and in Illustrator under Window>Separations Preview. The figure below shows the previous example with the black channel turned off.
If you have any questions regarding properly setting up your files for print, feel free to contact Phillips Printing prepress department by email or call 888-ask-phil.