The additional units found on many presses can be used in many ways. Touch plates, which are also known as bump plates or kiss plates, apply an additional screened color to an image or a portion of an image, to increase, or bump up, color saturation and contrast or reproduce a color that is hard to capture using only conventional process inks.

Touch plates are often used for images with vibrant reds or blues, such as a child's red wagon or a deep blue sky, or in images with a wide range of hues that may lie outside the range, or gamut, of CMYK colors. Using a screen of the bright color you want to match along with CMYK inks adds to the intensity of the color and reveals more highlights. Applying an extra hit of black can deepen the contrast of the image. A touch plate of a metallic ink can help bring out the shine in jewelry or metal. A touch plate using a fluorescent ink can add an otherworldly effect to the image.

But there are good touch plates and bad ones. Because touch plates are most often used on a portion of an image, they need to be carefully blended in with the contours of the original--otherwise, the touch plated area will look like a cutout. Good touch plates also match the full tonal range, from light to dark, of the original image. Remember too that not all of the colors, such as metallics or fluorescents, that might be used in a touch plate can be accurately reproduced with current proofing systems. What you see on the monitor may not match what you see in the proof or on the press.

Sometimes, it's possible to achieve many of the same effects as a touch plate without using any additional units on the press. Instead, one or more of the conventional CMYK inks are replaced with different inks--anything from a more intense shade of a process color to four fluorescent inks. The switch can help to highlight a specific area of the image by making the dark blue waters of a lake even bluer, for example. But because the color is applied in place of a process ink, all of the image will be affected by the change, raising the risk of sickly skin tones and other unintended consequences.

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