Ink key and ink feed setting with color management software

Discussion in '4-Color Offset Presses +' started by Osama, Jun 2, 2021.

  1. Osama

    Osama Member

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    Hello everyone,

    I work in the prepress and I have frequent arguments with our pressmen regarding color management.
    My perspective: To set ink keys according to the suggested values from our software (PressPerCent) and then control overall ink through ink feed setting.

    Pressman perspective: Since the printing plates already have the required screen percentages, we should set all ink keys equal (that is 100% cyan should be the same all across the sheet when read with a densitometer).

    If I follow PressPerCent recommendation then lets say I set ink key 1 to 25% and ink key 5 to 50% then a color strip of 100% cyan will give a different density / LAB value in front of key 1 and key 5
     
  2. turbotom1052

    turbotom1052 Senior Member

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    As a 35 plus year sheetfed veteran, I will tell you this... The best starting point for the presses intial ink key settings should be the CIP data the pre press department sends to the press, but ONLY if that CIP data has been arrived at through a thorough blueprinting of the press to your pre press department. This "blueprinting" I speak of, is rarely going to be something that the average pressman, or the average pre press tech will arrive at working together. In most instances it will come from calling in outside help. I would reach out and partner with your plate supplier to have them supply someone to come in and set it all up. This person would be someone who is well versed in both the pre press process and multicolor presswork. Plan on a long work day of testing, with availability of a decent amount of gloss coated paper, silk coated paper, and uncoated paper. To rush this process, or to not be generous with the allowable paper, will not work out well for you.
    In anticipation of this testing you will need to be certain that the press is ready to print to a high standard, with decent rollers that are set correctly, and good blankets that are properly packed. You should have on hand a good densitometer, that has a recent and known calibration. The form required for such a test should be provided by the person who is overseeing the testing.
    Even after a thorough blueprinting of the press, it should not be expected that the initial CIP data is able to print every single job without pressman intervention. CIP data, even at its most accurate, should only be considered a starting point.
    Its been my experience that the best results will come from matching the plate output to the way that the press prints and to the inkset you are using.
     
    Last edited: Jun 6, 2021
    mrheidelberg likes this.
  3. mantman

    mantman Senior Member

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    I think your pressman needs to think over his claim a bit. You cant put all ink keys at say 30% and expect a full solid, to be at the required density next to light halftone -meaning halftone correct whereas solid will be lighter-.

    As Tom said CIP data, give you a starting point and you tweak it job by job, till you reach a happy medium and play light piano to make it right.
    Its unavoidable to have fluctuations of densities across the sheet, as long as it does not, surpass a certain threshold -0.05 imho-.

    Tom i cant agree with you more but unless management buys same paper and ink you can never be stable and consistent.

    Even if you manage to map your Lab with density and TVI for all 3 papers -gloss/silk/uncoated-, i doubt you will get the same results with another brand of paper along with ink.

    In my opinion, if your employers decide to stabilise their printing, they should buy ONE brand of paper for each type and buy ONE brand of ink.
    Only then can you blueprint/map your process, from platemaking to CIP data and print Lab-density-TVI. Also you must choose what standard you want to follow, fograXX or house proof.
     
  4. alibryan

    alibryan Senior Member

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    (Post Deleted)
     
    Last edited: Jun 10, 2021
  5. Travis Young

    Travis Young Member

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    If the pressman is achieving the correct densities across the colour bars at the bottom of the sheet, then he has done his job the way I see it?
    The percentages set on the keys will be proportionate to the amount ink required to reproduce the image on the printed sheet in the area on the sheet relative to that key.

    "If I follow PressPerCent recommendation then lets say I set ink key 1 to 25% and ink key 5 to 50% then a color strip of 100% cyan will give a different density / LAB value in front of key 1 and key 5"

    Would that not simply imply the image on the sheet in line with ink key 5 is larger than the image in line with ink key 1, therefore requiring the key to be further open to achieve the correct density?
     
  6. turbotom1052

    turbotom1052 Senior Member

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    It saddens me to see that all a pressman needs to do is achieve the "desired numbers", in order for his job to be considered done!!! This is the exact sorta mindset that taken the craft out of printing. There was a time when a pressman was required to actually be able to evaluate color and determine what an image needed to match a proof. I can remember working for a company that often gave you plates without any color bars at all, and it was expected of you to match color. I guess this is the reason that current multicolor pressman salaries have actually gone down over the last decade or so, instead of keeping up with inflation. These days a persons value as a pressman is more judged by how willing he is to work with a broom stuck up his butt, so that he can sweep the floors as he is running around the press, than in the knowledge he brings to the table on how to actually lay ink on paper!!! So glad that I am retired and not having to run around with that broom in my ***.
     
  7. alibryan

    alibryan Senior Member

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    In the press side software, most modern day presses have conversion tables for the different papers, inks, coatings, etc. These are usually set up by the press manufacturer’s technicians/demonstrators that installed the press. It’s also possible for qualified operators to do it, as long as they simply understand how it all works.... (in my experience, some operators do, but many don’t). What that means is that even with your ink key zone program in prepress (PressPerCent?) sending the plate image (percentage) requirements to the press, that information should still filter through a pre made conversion table. Because, and depending on the variables of any given job (mainly paper), not every job will need to convert the same way. So if you’re either not aware of, or simply aren’t using different conversions for different papers, the PressPerCent values that are sent to the press aren’t going to be accurate for every job anyway, no matter what you or your operator do.
     
  8. Travis Young

    Travis Young Member

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    Yes that's all fine and I agree but in the interests of consistently providing our clients with quality work, that is how the system is intended to work.
    I've done plenty of jobs where I've had to compensate to match the proof. We all have.
    But wether it's CPC calibration, old fashioned dot gain or anything in between, it's an indication that the pre press process can improved.
     

  9. turbotom1052

    turbotom1052 Senior Member

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    Theres always room for improvement in all manufacturing processes, but what Im referring to here is the disturbing trend that has a supposed pressman unable to print, if his closed loop inking system goes down, or if his densitometer craps the bed. Ive actually seen guys panic when they had to go old school, and manually set fountains, or run the press without the help of their closed loop inking technology. And the way that they compensate for their lack of experience, is to run around like a chicken without a head, running a multicolor press all alone, all the while jumping up and down off the presses catwalks, drenched in sweat so that that they can produce 20 jobs in a shift. Then when the inevitable job or 2 gets rejected by the customer, they just put their heads down and humbly take the spanking that management dishes out.
     
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