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If you number the samples in your photo from left to right, 1-6, there are 3 close pairs. 1 & 5 yellow 2 & 6 magenta 3 & 4 blue Can you provide a Delta E (DE, dE) for those pairs?

The defect you show in the photo is a long vertical streak? Is it visible prior to printing, perhaps as a gloss difference? If you cut the sheet down so you can feed it through rotated 90 degree, is streak still there in the same orientation (machine caused) or did it also move (paper caused)?

Can you provide close up photos, without glare, of good vs bad?

Most modern newspaper press use web offset (cold-set) lithography. The ink transfer from the plate (metal) to the blanket (rubber) then to the paper. If the rubber blanket is damaged, sunken inward, it will not transfer ink from plate or to paper. This is often called a smash or ding.

Whatever method is used, always note the version of the formula fan guide. Over the years, there has been revisions/changes. Mixing the correct formula recipe is no quarantine of a close color match (Delta E) mostly because of the substrate.

Search previous posts about this same topic. Need thick ink film to get opacity. Multiple passes, dry trap, flexo relief plate, UV, silver base, screen print, foil stamp, etc.

To be precise, UV inks don't "dry", they cure. How did you evaluate UV Cure? Physical rub test, Chemical resistance. Are UV lights guarded/shielded so no light (radiation) is striking or "Flashing" the plate and curing there? Dry-up/catchup, tinting/toning, scumming/sensitivity all look...

Ask your vendor's (ink, paper, device) if they profile for you as a free service?

You didn't mention what the specific quality issue is? Image sharpness from poor focus? Loose fit in press plate clamp?

Did roller vendor recommend EPDM composition?

A packaging structural designer or die maker should be able to answer that. I think a higher number of smaller perfs will be "stiffer" and have more memory. A folding carton packing QC lab often has a machine to measure force to open & close folds. Also, on the folder/gluer, how much of a...

Magnus, I agree with your statement. When an ink guy tells a press guy to run to a lower density, that might be interpreted as meaning a thinner ink film thickness (IFT). The ink fountain blade keys or ball/ductor sweep will be less because it's stronger. Doing a side-side ink draw down (Little...

Low cost solution is bring both characterization data sets into Excel and calculate a Delta E for each pair of patches (1,617 if IT8.7/4). Then do some basic stats for average and standard deviation. Could even make a histogram.

Check the grain direction of both your and their samples? Are they using any perforations instead of crease/scores?

Outsource to a trade/packing printer who has a press with an UV anilox coater in unit #1 to lay down opaque white first. Use a flexo relief plate. If customer doesn't care about how the inside of the box looks, print on white litho wrap sheet to match kraft color, then emboss corrugate texture...

When you run an ink to a lower SID it usually for 2 reasons. 1) It is stronger, has more pigment concentration. 2) It has more dot gain, so you are compensating instead of making a new curve.

Yes, my brother Joe unfortunately passed away in March 2018 from a severe stoke. At the time he was working for Heidelberg after being at GATF in Pittsburgh.

Do you know the Lab values of your current ink set, as well as SID (solid ink density) & TVI (tone value increase). Curious, if you changed ink vendors with regular inks, would you use the same old ICC profiles and plate curves or would you re-fingerprint?

You mention a long-time frame, over years. I assume you have a standard test image printed from then vs now, with exactly the same settings and conditions. How do you know your media paper is stable and not causing the color shift?

How about this for Xerography basics?