This story courtesy of PaperSpecs.com.
In most cases, printing on a colored stock means printing on an uncoated stock — metallic stocks are mica coated (a mineral consisting of shiny, transparent crystals) and fall into a different category — which means you are facing the challenge of dot gain, as well as the paper’s hue.
Depending on the color of the paper you choose, CMY and K will have a dramatically different look. Printed on a cream stock, they have a warmer feel; printed on a paper with a blue or cool hue, the image highlights will be the color of the paper — reducing the image’s contrast.
You might be using the same ink and the same coverage, but offset inks are transparent and allow the paper they are printed on to “bloom through.” This is not a problem when printing on a white stock, but the darker the paper, the more it will influence the perception of the colors printed on it.
While you should always take a look at samples of similar projects on similar stock, they are no indication how your files will print when on press.
“A drawdown is a great way to see how inks look on a specific stock,” says Allen Strohmeier from Cenveo Anderson Lithograph in South San Francisco. “Larger printers offer this service in-house, and a smaller print shop can get samples from their ink supplier.”
Drawdowns are great for solids but don’t let you judge how a full-color image, or any screened image for that matter, will look on the sheet.
If it’s a CMYK job on a light-colored stock, ask your printer to run a few sheets of your chosen paper at the end of another print run.
When going this route, keep in mind that it takes 50 to 100 sheets of the stock in question to give you a good evaluation.
Most importantly, the images of the original press run naturally have not been adjusted to allow for your paper’s hue; i.e., printing on a cream or ivory sheet will give your CMY and K a warmer tint. To allow skin tones to appear as natural as possible, yellow should be subtracted from the image’s midtones to compensate for the stock color.
And don’t forget timing. You have to wait until your printer actually runs a similar job with the same sheet size as yours to receive an accurate evaluation.
So what do you do if you don’t have the time to spare?
If you can’t wait to test your stock at the end of another print run (a similar ink coverage with the same sheet sizes might not be scheduled for another week or two), consider the option of getting a one-off print from a digital press, such as the Indigo (the digital press closest to offset) on your stock. This is not a perfect match, but it gives you a good indication of what you can expect on the actual press run.
The Under-Printing Solution
If your project includes full-color images on a medium to dark stock, under-printing a white opaque ink will help you keep the colors vibrant.
White inks, as well as all metallic inks, are by nature opaque and allow offset inks to sit on top of them — literally. Two or three hits of white or silver ink give you the best support for your images.
Wet-trapping: For a subtle look, run the opaque inks in line with your CMYK — not preferred.
Dry-trapping: Wait for the opaque inks to dry before running the CMYK inks to allow for maximum “pop” or contrast of your images — most preferred.
UV inks: Another option is to use UV inks, which are dried on the run between each print cylinder, but not every printer has the equipment and other than time, there might not be any overall savings in comparison to dry-trapping.
If under-printing is not an option for you and you are printing on a light or medium colored stock, add a small percentage of silver ink to one of your colors. It will enhance the opacity of this specific color and give your images more hold, although silver will add a slightly graying effect to your color.
My personal favorites when it comes to printing on uncoated colored stocks are the special effects that are possible in combination with a tactile experience when holding the piece.
Colored stocks can make a one-color job look stunning. Any metallic ink (or white opaque) is ideal for printing on dark papers, but silver is the most effective because of its inherent reflectivity. Just remember, two hits give the best coverage.
Printing opaques only in specific areas to highlight aspects of your image will create an astonishing effect… and make your clients notice.
Or create art in and of itself by selecting the one channel of your CMYK image that gives the most desirable effect and print it as a solid, a posterization, a reverse or… the possibilities are endless.
“The key, as with any print job, is to get your vision of the project in line with what is possible with pre-press and on press,” says Allen Strohmeier. “Choose a printer who has experience with the kind of effect you want to achieve and who believes in your project as much as you do.”
To get a great idea of what is possible on colored stocks, take a look at Domtar’s Answer Pack A, which compares your images on white stock with the same images on colored stock and shows special effects as well.