strange color differences

[Bobmorli]

Hi all,
Just looking if anyone has anymore suggestions regarding a problem we've been having for about 6 months now.
We notice that when we do a rerun of something we printed 2 months ago, we have a color differnce that is mainly visable in the magenta. However nothing has changed to our general setup. RIP / DotGain / Plates / TopSetter / Press & Presscalibration / ink, it's all the same as 2 months ago.
We've done all kinds of tests and can rule out any prepress mistakes. I'm trying to see what possible things could give us the effect on the press side.
We notice that once we're up and running (let's say after 2 to 3 thousand sheets), our color comes closer to the previous run.
According to the pressmen, nothing has changed at their end. PH value / water-ink balance / printspeed / pressure, is all the same.
Any idea's?
Thanks in advance!

 

[Lukas Engqvist]

Are you comparing 2 months old prints with the wet print, or are you comparing data from 2 months aggo with data from today.
Also some more details on your configuration may help.
Do you have TVI data so you can verify if it is the colour of the pigment or the dotgain that has changed. Is the stock the same.

 

[Bobmorli]

We are comparing prints from 2 months ago with wet ones and with ones we left to dry for a day or 2. So dry and wet.

Details on our configuration:
Artpro -> Nexus RIP -> Heidelberg Topsetters ->Heidelberg Speedmasters:
CD74 (1 eight color / 1 six color)
CD102 (1 six color / 1 five color)
XL105 (2 five color / 2 six color / 2 eight color)

What do you mean with TVI data? The dotgain is still the same. Has been the same for more than a year. Pigment of our magenta ink was changed in january but problems started later.

 

[jlind]

Why did you change the pigment of the magenta ink? Not that this has anything to do with the strange color differences. What is strange about what you see? Some visual descriptions would be useful. Are you running Image Control on all those Heidelbergs? Is there a water based coating on those jobs?
John Lind
Cranberry Township, PA
724-776-4718

 

[Bobmorli]

John,

What we see:
If we compare what we print today with what we printed 2 months ago, we notice that there is a color difference, mainly visable in the magenta but also in the black and cyan. Lets say we have a tomato. 2 months ago, this tomato looked very tastefull. When we print that same file now, with the same densities, we notice the tomato is not that tastefull anymore. Either it is not red enough or it is to red. We see that our printed dots are either smaller or bigger. Generally, after 2 or 3 thousand sheets printed, we can get closer to the color we had 2 months ago.
I'll look into getting a scan online so you get a visable view of the problem.

Thanks!

 

[ajr]

Have you checked the chiller units on the presses (for the rollers),, or your fount solution. It could be a heat problem (or too cold).

AjR

 

[Lukas Engqvist]

Either it is not red enough or it is to red. We see that our printed dots are either smaller or bigger. Generally, after 2 or 3 thousand sheets printed, we can get closer to the color we had 2 months ago.

If you have the same dotgain you cannot at the same time have printed dots either bigger or smaller. Dot gain means that the bigness or smallness of the dots is the same!
How do you measure your dot gain?
Where do you measure it. Record reference values on file, ripped file, (film), plate and paper. If you get a variance trace the variance to the step where error occurs.
There are many things that can affect the dot gain which produces a tone value increase). Find out what is causing that the size of the dots varies. Is it temperature. Humidity. Viscosity of inks? Chemistry? At what stage is the instability?

 

[Alois Senefelder]

re - Color Variation

re - Color Variation

Hello, 1- Have you changed Press Blankets ??

2 - Changed Paper Brand or Supplier ???


Regards, Alois

 

[Jim Restle]

Similar Issue Here

Similar Issue Here

We're facing a similar issue at my company. Our pressman can't get a work-and-tumble job to match from one side to the other, so naturally the focus turns to prepress.

The second time through press the photos are "redder" even though he says his numbers are identical for both sides of the sheet.

Jim

 

[richck]

We're facing a similar issue at my company. Our pressman can't get a work-and-tumble job to match from one side to the other, so naturally the focus turns to prepress.

The second time through press the photos are "redder" even though he says his numbers are identical for both sides of the sheet.

Jim

I think i would be looking at the paper Jim,we have had a similer problem,, I have put it down to the conditions in the pressroom and the paper storage prior to been on the the press, I'm a presssman and i saw no way it could be prepress.

 

[Bobmorli]

Alois,
We don't print on paper but on polyprop. We haven't changed supplier. Our blankets have been the same kind for the last 2 years now so that would suprise me to be the cause.

At this moment we've excluded prepress and ctp after measuring our plates dots / tiff files and such. The storage of our polyprop may be an influence. That's the only thing that has really changed.

Thanks for the tip richck!

 

[chknlegs]

re: strange color differences

Just a suggestion:

Have your ink supplier give you draw downs of the cans of ink they ship you. Different batches may have a different LAB value which will result in different colors on reprints. You can check this with a spectrophotometer. I've had this happen to my on a few occasions.