Re: GRACoL densities
Re: GRACoL densities
- Subject: Re: GRACoL densities
- From: Terry Wyse <email@hidden>
- Date: Sun, 1 May 2005 08:53:41 -0400
I concur with Ray. I did a press profiling job a few months ago where I
had access to an X-Rite ATS scanning spectro unit. We did the run to
GRACoL SIDs and I scanned/measured the color bars wet and then every
couple of hours for 24 hours after that. With THAT ink set we saw cyan
drop about .07 and the magenta only about .03. Black dropped nearly
.15. We then changed ink sets and ran the test again (same stock). THIS
time the CMY only dropped about .03 and the black about .07-.10. So it
varies depending on ink at least.
Since it's really not practical to wait a couple of hours to find what
the dry-back is, I simply run the SID about .03-.05 high. What I REALLY
watch while running is a set of gray balance targets to make sure the
densities are in BALANCE. I find that as long as the densities are
within about .10 of the target but that they are in balance with each
other (all a bit high or a bit low), I'll get good results. As far as
the black, I'll have the pressmen run the black as high as they are
comfortable with (typically 1.80-2.00) while keeping an eye on print
contrast to make sure it doesn't get out of hand.
Beware of the instrument you're using also! I've run into several shops
lately using polarized densitometers (typically Gretag D19C w/ Status
T/P filters). Cyan and magenta will typically read .10-.15 higher with
the POL filter while yellow will be pretty close. Black on the other
hand can easily read .25-.35 higher or more! Because of this, I insist
on using my Gretag SpectroEye (Status T, no filter) during the press
run and then back into the numbers they should be using with their
polarized unit later. I've also found that X-Rite 500 series
spectro-densitometers will read about .10 higher than my SpectroEye
even without polarization. Personally, I think inter-instrument (or
inter-vendor?) agreement is the industry's dirty little secret. I've
even been to shops that have a mix of Gretag and X-Rite units of
different vintages (X-Rite 528 and older 408s for example or perhaps a
SpectroEye and D19C) and NONE of the units will agree within .05 of
each other even after careful calibration. So, for better or worse, my
SpectroEye becomes the reference unit at least while I'm on-site. Since
my SpectroEye TENDS to read lower compared to other instruments, I'm at
least confident that, even after dryback, we'll have densities that are
pretty close to the targets as measured by other instruments.
Later,
Terry
On Apr 26, 2005, at 12:17 PM, Ray Maxwell wrote:
Hi Roger,
In my experience it varies with press, ink, and paper. You have to
do wet measurements and then measure again dry. You then calculate
your own wet target densities or dryback.
"Your mileage may vary."
Ray
Roger Breton wrote:
Ray,
Are you double sure it's dry?
Never mind, Ray. I just found the reference at the bottom of page S2
of the
v6.0 2002 book : "Ink density are dry". But then they add: "Dryback
values
are included". What do they mean by that?
Take Grades #1 & #2 in that table on page S2. Under Solid Density,
they have
1.70 for the black. Black density, I found, drops the most when it
dries. So
in order to achieve 1.7 dry one has to aim for 1.8 or more wet. But I
fail
to see what "dryback values are included" could possibly mean in this
context? The old SHoPS GATF study included tables for dryback but
there is
nothing like that here.
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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