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For a number of years I’ve been seeing online (web-to-print) offers in which you can print your photograph or artwork onto metal. This is based on inkjet printing. It also takes advantage of the reflective nature of metal to enhance the appearance of your photo or art, to brighten it, and to give it an otherworldly sheen.
I find this interesting because it calls to mind a number of other approaches I have seen over the years to enlarge the number of distinct, printable colors available with a particular commercial printing technology.
The Hexachrome Process
About thirty years ago one of the commercial printing vendors I worked with (I was an art director/production manager for a non-profit government education foundation at the time) had installed two technologies relevant to this discussion: Hexachrome custom printing and the substitution of CMYK inks with anywhere from one to four fluorescent inks.
All of this was based on the limits of offset lithography. CMYK inks (cyan, magenta, yellow, and black) combine to create only a limited portion of the visible light spectrum. This is called the “color gamut.” Visible light (what you see outside in the sun) provides the widest color gamut of distinct colors. RGB (red, green, blue) phosphors that create color on a computer monitor or television screen produce a smaller color gamut. And the smallest color gamut is created with ink, paint, or toners (i.e., CMYK pigment on a substrate).
These colors (in the case of offset lithography) are transparent inks (usually printed in halftone dot patterns laid over one another and then slightly angled to keep dots of the four process colors from producing visible moire patterns). The percentages of these colors (as reflected in the size of the halftone dots) when seen together create the impression of color in the eye and brain of the beholder.
Because the offset lithographic color gamut is smaller than that of a monitor (or the visible light spectrum outdoors), it has been a goal over the years to find ways to expand the color range. Back when I was working with the aforementioned printer delving into Hexachrome color and replacement of certain process colors with fluorescent inks, this was how they attempted to extend the color gamut.
Hexachrome added orange and green to the normal cyan, magenta, yellow, and black inks. More specifically, when separating a photograph (for instance) into the usual four printing plates needed for process color printing, this commercial printing supplier would actually separate the photos into six halftone images. Doing so would add two of the secondary colors (orange and green) into the mix and therefore enhance anything containing these two non-CMYK hues, producing (for instance) vibrant blues and purples when combined with the CMYK inks.
You may want to compare this offset lithographic custom printing technique to today’s large-format digital inkjet printing technology, in which multiple inks (such as the usual cyan, magenta, yellow, and black, along with light cyan, light magenta, and sometimes red, green, blue, orange, and violet—or any combination thereof–for up to about ten or twelve inks) expand the inkjet color gamut beyond that of traditional offset lithography.
Touch Plates, Bump Plates, and Kiss Plates
Two things to remember when using commercial printing techniques with an expanded inkset are that you need more than four inking units on your offset press (so the price-per-hour to run a larger press, like an eight-color press, will rise beyond that of a four- or six-color press) and you can’t accurately proof such a job using traditional four-color proofing devices.
That said, and in spite of the fact that Hexachrome has not been a familiar name (to me at least) since I saw it in the 1990s, printers will add colors to your process ink work if you ask them to do so. These colors (with one plate for each additional color) have been referred to as “touch plates,” “kiss plates,” and “bump plates” because they bump up an otherwise subdued or non-reproducible hue. They also increase color saturation and contrast, so the effect can be quite attractive, and can in fact make a particular part of an image (like a child’s red wagon) really jump off the page.
To do this kind of work requires a skilled prepress operator, because you don’t want the transition between the additional color and the surrounding colors to stand out in too stark a manner. You don’t want obvious edges.
White and Silver Ink
The same approach needs to be taken to the underprinting of white or silver ink.
If you are printing on an uncoated, tinted sheet (let’s say a cream stock, for instance), the normal process colors will do two things. They will seep into the paper fibers, which will dull down the color, and (since they are transparent) the process color hues will be changed to a certain extent by the color of the paper substrate.
Printing a white background (graduated intelligently to avoid a “cut-out” appearance) will improve the color fidelity of the overprinted inks (they won’t shift due to the color of the underlying paper), or if you are printing a photo of jewelry, for instance, you can give a metallic sheen to the printed image by using silver ink rather than white ink for the underprinting.
Again, keep in mind that the background needs to be sensitively created with a wide range of tones (light to dark) to make it look like part of the overall color image.
Fluorescent Inks
A similar approach to adding silver or white ink to an offset printed job is to replace one or more of the four process colors with fluorescent inks.
The same printer I referenced earlier that was experimenting with the Hexachrome process (a Pantone, Inc., invention, by the way) made its own set of process colors with the same goal in mind: to augment the printable color spectrum. In this case, this printer would add fluorescent inks (anywhere from one to four fluorescent replacements for the CMYK colors, depending on the result the printer wanted to achieve).
That said, it is possible to replace a process color with just a more intense version of the same process ink rather than an actual fluorescent ink. But in either case, it is important to note that changing the color of one process ink will affect everything in the job—all photos, colored type, and solids and tints—and this may adversely affect such things as skin tones, creating an otherworldly effect. This can be made even more problematic given the difficulty in accurately proofing such ink substitutions.
The Takeaway
That said, you may have more options than you had thought for your commercial printing jobs if you’re willing to experiment with the inks. When I was an art director there were sample books you could get from printers and paper merchants showing the specific kinds of effects possible with metallic inks or fluorescent inks. These included color images printed on different kinds of paper (uncoated vs. coated, for instance, or different colored hues of paper).
Assuming you can still get these sample print books, I’d encourage you to do so in order to show your print provider the exact effect you want to achieve. And don’t assume all printers will be equally skilled in custom printing fluorescent and metallic inks. Ask your printer for samples of work he has actually produced as well as paper and ink sample books.
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