Press Fingerprinting in FTA Oct. 2013

Testing The Limits

Best Practices For Press Fingerprinting

Just like the tips of our fingers, the way each press
lays down ink is unique. Each press prints at different
speeds, pressures, dot percentages, etc. But printers
must print customers’ products accurately and consistently.

This is why fingerprinting is so important. Today’s printing
industry is all about the customer. The newest and fastest
presses, the best proofing processes, the most efficient workflows—
none matter if the customer is not happy. If printers
do not test the limits of their printing process, to know exactly
how their press prints, they won’t be able to deliver the results
customers expect.

Carey Color has spent a lot of time working with printers to
help them adopt elastomer sleeves as their preferred in-theround
material. It’s come to rely on press fingerprinting and
developed a set of best practices for the process. The goal
is to help the printer control pressroom variables, achieve
tighter tolerances, improve print repeatability and match the
proof consistently. How do we do that?

It starts with building a sleeve and continues by establishing
a database of tightly matched parameters for each sleeve
and fingerprint. We run an individual fingerprint for each set
of variables (press, ink, substrate, etc.), so that when those
variables change, we know what the printed piece is going to
look like

FINGERPRINT FILE

When building a fingerprint file, it’s safe to only include the
graphics, tables and linescreens that any press will print effectively.
But you’ll typically find with a good profile that not all
portions will succeed. Why? It’s important when building a file
to include linescreens higher than typically printed, reverse
copy smaller than usual and highlight dots you typically cannot
hold with the current process.

When simply preparing for something like moving from
one manufacturer’s polymer plate to another manufacturer’s
polymer plate, fingerprinting to determine minimum dot, dot
gain, line screen and registration is the standard practice.
But when embracing new technologies like elastomer and expanded
gamut, the goal is to build a fingerprint that reaches
beyond the boundaries of what you’ve printed successfully in
the past. With new technology, it’s good to know the threshold
and sweet spot.

It’s important not to take the safe route—If a print shop has
never printed higher than 120 linescreen, it should put 133
and 150 on the fingerprint, so that at some point, the print will
fail. By doing this, a printer can understand exactly where
its limitations lie. The printer may find that printing a higher
density or a finer linescreen is a real possibility when it hasn’t
been before.


When fingerprinting for elastomer, include target areas with slight
variations of dot height and shoulder angle. Include a target with
a slight bump curve in the mid tone, push targets with the highest
possible linescreen ruling and feature text and reverse text down to
one point. Story and art: Carey Color Inc.


PRODUCT ION CONDITIONS

Don’t roll out the proverbial red carpet when fingerprinting.
The goal is to print in the same environment and process a
printer normally would. This will create an apples-to-apples
comparison between the fingerprinting job and a typical job.
When preparing for a fingerprinting job, take these steps into
consideration:

  • Be mindful of what average printing conditions are and
    attempt to maintain them for every print job
  • Fingerprint with the same ink, density, pressure, speed
    and operators normally used
  • Mount the sleeves, bring the press up to speed, set impression,
    check density and pull sheets for evaluation

A typical 1-color fingerprint should take less than 20 minutes
from start to finish. The goal is not to create a product
that cannot be reproduced on a day-to-day basis; rather, the
goal is to develop a process that offers the best quality and
repeatability on re-runs and in matching proofs.

Key components should be documented and recorded for
future review. One option is to build a database for a printing
process so future runs will be engraved and proofed with
curves built from data collected in prior runs. By continuing to
take readings from live production, a printer can later tweak
the proofing and engraving curves.

FINGERPRINT READING

After it is printed, it is important to precisely read the
fingerprint and know what to look for. Here’s a breakdown
of Carey Color’s process—remember, we are not always on
the pressrun and not always capable of making density and
impression changes while the sleeves are running:

  • Visually check for imperfections like streaking or banding,
    ink bridging and impression
  • Evaluate visual consistency of ink laydown and density
  • With a densitometer, measure dot gain in the following
    areas:

    • 1 percent to 5 percent
    • 25 percent
    • 50 percent
    • 75 percent
    • Solids
  • Enter the readings into software that plots dot gain characterization
    curves. It’s important to take readings from
    four places across the sheet and then allow the software
    to determine an average

At times, run several different sleeves made with different
elastomer compounds. The purpose of this is to find the best
printing combination. By making changes in compounds and
anilox a printer is able to pick the material and durometer
best suited.

The goal in this first process is to build a dot gain characteristic
that will match General Requirements for Applications
in Commercial Offset Lithography (GRACoL) Standards
(ranging from 18 percent to 25 percent dot gain). This process
will be better defined after creating a 4-color fingerprint.

BUILDING in 4-COLOR

Once a curve has been built, the dot percentages should
translate across all channels. We then print a 4-color fingerprint
to create International Color Consortium (ICC) Profiles
for proofing and monitor calibration. In this process, the goal
is to get the printer to G7 standards using CMY-to-black conversion
patches. A typical target is a Color IT8 7.4.

We then measure the 4-color fingerprint to verify dot gain,
wet traps and overprint for the purpose of building a profile
for that specific press, substrate, ink and so on. ICC profiles
are then built to define the achievable color gamut of the
press with a 4-color process. The next step is to correlate the
relationship between the input data and the printed result and
develop a proof that can match the press consistently.

What is most important to realize—and this is where most
ICC Profiling falls short—is that just because a proofing target
is within G7 (or any other proofing standard) specification, the
proof may not be up to standards visually. Even if all colors
are within a Delta E of +/-2, seeing the visual deficiencies and
adjusting the proof to fix those deficiencies requires specific
levels of expertise. This is why including common graphics
and images is important in a 4-color fingerprint file: To allow
calibration of proofs for a visual match in addition to a specification
match.

There are many challenges in this step. For instance,
building a profile from a paper proof to a paper print is much
easier than understanding how proofing on clear material
overlaid on the printer’s substrate (like foil) will translate to
the printed piece. This is where experience comes into play.
Building a proof, when proofing onto the printed substrate
isn’t always an option, is tricky. The knowledge of an experienced
specialist is essential to create a match.

EXPANDED GAMUT FINGERPRINTING

As more and more printers start to print using a standardized
7-color process, fingerprinting best practices remain
as important as ever. Continuity and consistent horizontal
density across the press sheet and from corner to corner is
key for consistent fingerprinting with expanded gamut. This is
important because in a 7-color process, inconsistent densities
magnify just as much, or more than, traditional CMYK.

The evaluation process is similar in expanded gamut,
but due to the complexity, specialized software is required
to build the achievable color space and develop proofing
processes to match the press. It is important when switching
to expanded gamut to choose auxiliary colors that best match
the color gamut of what is typically printed: Choose from
green, orange, red, violet and blue to achieve the widest color
gamut.

Also, develop gray component replacement standards on
prepress files to minimize ink density on the printed piece.
Files that contain large Pantone solids and vector art are gray
component replacement converted more aggressively, while
CMYK images are converted less aggressively. This will get
fingerprints up to color more quickly and consistently and
result in better matching the proof to the printed piece.


Continuity and consistent density horizontally across the press sheet
and from corner to corner is the key for consistent fingerprinting
with expanded gamut.


ELASTOMER FINGERPRINTING

With laser-engraved elastomer sleeves, variables like dot
height, dot shoulder, relief depth and shoulder angle can be
controlled. Therefore, when fingerprinting for elastomer, it
is normal to include target areas with slight variations of dot
height and shoulder angle. Because elastomer generally
prints sharper, include a target with a slight bump curve in the
mid tone, which is usually a credible starting point.

Push targets with the highest possible linescreen ruling and
include text and reverse text down to one point. The result
is usually a very clean print with high ink densities and very
predictable dot gain, which allows printers to print highlights
more consistently by reducing impression/pressure.


KEY
1. Linescreens above and below your standard linescreen
2. Tints or images with sufficient highlights, shadows, mid tones and solids
3. Barcodes with different BWRs
4. Slur charts
5. Small to large positive and reverse copy (down to one point in most cases)
6. Vignette gradation target
7. 100 percent – 1 percent left and right impression check


THE NEXT ITERATION

About 90 percent of the work for fingerprinting is done
once the multichannel fingerprint is created. Proofs should be
matched on press and with correct plate curves and proofing
profiles, this should be very achievable. But there is always a
need to evaluate live production.

New projects may reveal deficiencies in the proofing
process because of unforeseen color combinations or visual
inconsistencies that were not detectable with stock images.
This is especially important with the first few post-fingerprint
jobs.

Periodically providing printed material to a separator is
key to continual improvement. It is vital to develop a proofing
and printing process that, while consistent, can be adjusted
slightly as new information about how the press lays down
ink is discovered. Then, the goal is to run those jobs the same
way, every time they are on press.


About the Author: Carey Color Inc. is a full-service digital
imaging company headquartered in Sharon Center, OH,
with locations in Illinois, Wisconsin and the U.K. It employs
more than 75 experienced prepress craftsmen. Carey Color
specializes in manufacturing laser-engraved plates and
elastomer sleeves for the flexo, dry offset, emboss and intaglio
industries. It also provides prepress services for direct
mail catalogs, packaging, flexo and dry offset in addition to
commercial photography and offset platemaking. To learn
more about how Carey Color can help in the fingerprinting
process, contact 1-800-555-3142 or visit www.careyweb.com.

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