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.]