Printing & Design Tips: August 2004, Issue #37

What You Should Know About Printing Ink Drying Time

Has your printer ever called you to say your job will be a day late because it is taking longer than expected for the ink to dry? What should you know about ink drying time to help you plan your printing schedule?

First of all, understand that your printer is making a reasonable request. It is prudent to let ink dry before folding a job to avoid streaking or "offsetting," in which wet ink smears or transfers from one sheet to an adjacent sheet. Some inks dry faster than others, as do some substrates such as synthetic and plastic papers.

Heavy ink coverage (solids and bleeds) on uncoated paper or matte stock take longer to dry, particularly if the ink mixture includes any reflex blue. A print job also dries more slowly on a humid day.

If you have taken all this into consideration when scheduling your job, you can understand and accept your printer's request for more time. If a quick turn-around is needed, you should choose colors other than blues and purples, and/or choose a gloss sheet as a substrate.

If these options are not appropriate in your case, you could ask your printer to coat your job with a varnish or aqueous coating. These coatings cover the ink as it cures, minimizing scuffing and allowing your job to progress through the printing plant more quickly.

Converting Images to CMYK

When you scan a photo, it usually comes into your image editing application--such as Photoshop--in an RGB color space. The same is true for an image from a Photo-CD or a digital camera. RGB (red/green/blue) is the appropriate color space for colors composed of light rather than ink, such as images on a computer monitor. Work you produce for the Internet would therefore be saved in an RGB color space, perhaps as a JPEG.

On the other hand, when creating art files for a four-color brochure, you would need to save your image within a CMYK color space, or you will not get the four color-separated negatives or plates you need to drive a four-color printing press. Although your printer will probably catch this error in preflight, he may charge you for system time to make the conversion. At the very least, this error would add unnecessary time to the prepress component of your job.

Forgetting to change images from RGB to CMYK is a very common error among designers. It is easy to forget, since most desktop ink-jet proofing devices will convert to CMYK on the fly, while you are printing, rather than giving you an error message noting that your images are in the wrong color space. A useful trick to ensure that you supply accurate files is to print color-broken laser proofs. If your application doesn't print something on each of the four pages representing the cyan, magenta, yellow, and black plates, you need to go back into your files and make an adjustment.

FM Screening

Until recently, halftones were made up of a grid of equally spaced dots that varied in size. In a dark area of the halftone, the dots would be larger; in a light area, smaller. Since a four-color image is essentially four halftones set at angles to one another, the same variance in dot size would apply to color work as to black and white, providing equally spaced rosettes (patterns of the C, M, Y, and K dots). This is called amplitude-modulated screening because the size of the dots varies.

FM screening (also known as stochastic screening), on the other hand, is made up of much smaller dots that are all the same size but are randomly placed. In a darker area, there will be numerous tiny C, M, Y, and K dots. (If you're printing a black halftone, these will be black dots.) In lighter areas, there will be fewer dots. The dot frequency will vary instead of the dot size or amplitude.

In short, FM screening thus allows you to print higher resolution images with greater color fidelity, more control over ink density, minimized dot gain, and no moire patterns. Ask your printer about this technology. There may be a place for this process in your printing work.

[Steven Waxman is a printing consultant. He teaches corporations how to save money buying printing, brokers printing services, and teaches prepress techniques. Steven has been in the printing industry for thirty-three years working as a writer, editor, print buyer, photographer, graphic designer, art director, and production manager.]