bump curve

[asr]

i did linear print on a sheetfed press and measured halftones need to bump up rather than lower the curve, is this just normal? instead of a dotgain, i get dotloss of -4 to -6 on almost all units running cmyk.
hope some info be shared if i can proceed with the profiling with this results.

best

 

[Magnus59]

Can you share a bit more information about your workflow, how plates are exposed etc. Whether plates are positive or negative, wet plates or DOP?

 

[Cornishpastythighs]

What target ink desity were you running for your process colours. Is the ink your normal supplier or a new ink supplier (ink strength). Ink film thickness can sometimes affect dot size

 

[asr]

Can you share a bit more information about your workflow, how plates are exposed etc. Whether plates are positive or negative, wet plates or DOP?

will get more info in the production floor. will update

 

[asr]

What target ink desity were you running for your process colours. Is the ink your normal supplier or a new ink supplier (ink strength). Ink film thickness can sometimes affect dot size

cyan is already 1.6, magenta is 1.6, yellow is 1.45 and black is 2.00 - using greyback -(claycoated). ink is a well-known brand and i just initiated to do profiling and fingerprinting to have reference for all future jobs

 

[SheetSqueezer]

The first step is to measure the dots on the plates, so you know what you’re giving to the press. And no, what you’re describing isn’t just normal at all.

 

[asr]

The first step is to measure the dots on the plates, so you know what you’re giving to the press. And no, what you’re describing isn’t just normal at all.

plate is ensured to be linear. 5 is 5, 20 is 20, 50 is 50 and so on. and the resulting print is 50 is 44, 80 is 75. any idea why this happens. i tried doing c2s and almost same result, meaning i need to put more bump to hit the iso dotgain

 

[Magnus59]

Has your densitometer been calibrated? Is it set to the correct colour reading? Are you reading a solid area from the same sheet prior to reading the screen?
If all of the above are correct, then you most likely have a problem with ink roller settings, fountain settings or pressure. Check all of these before adjusting your plate curve.

 

[cementary]

I would suggest to start with dampening rollers. Check hardness and alignment to plate

 

[Asures]

Quoted - instead of a dotgain, i get dotloss of -4 to -6 on almost all units running cmyk.

For starters, measure the dot on the plate to verify where your starting point is. Is really doesn’t matter whether you start linear or not as your cutback curves are going to be calculated on L*a*b* values as you’re targeting grey, correct? (assuming your targeting G7).

Second, it sounds as though your dot loss may be coming from actual plate exposure. I’ve seen this far too many times. Try monitoring and measuring the densitiy on your screen tints. Running the same calibrated densities, if you see them drop but your solids are the same, that indicates premature plate wear.

Just my friendly .02

 

[gordo]

Also, check your printed halftones for signs of over-emulsification.

 

[chriscozi]

The missing elements to the discussion leading to relevant answers:

1. The Make/Model Printing press used?
2. The Plate Manufacturer/Type used?
3. The Platesetter used?
4. The RIP used?

Any/All of these facts MAY lead to different relevant answers to the original question.
Unless someone thinks 'alternative facts' will help? (snark)

PS - I would love to assist with a rational diagnosis of the problem.

 

[asr]

i will gather plate and press data and send here for all further analysis. thank you for all the inputs. i will just collect all the datas

 

[asr]

Also, check your printed halftones for signs of over-emulsification.

how to check over-emulsification sir? any pictures to describe this

 

[gordo]

how to check over-emulsification sir? any pictures to describe this

Before you do any curves you need to make sure that the press is printing properly, consistently, and repeatbly.

Hopefully you have one of these inexpensive microscopes so that you can view and photograph the dots on plate and in your presswork.

Look at the halftone dots on the plate. They'll look something like this:

The job of the press is to reproduce the dots on the plate on the press sheet. Properly done the result looks something like this:

Note that the dots are evenly dense across their surface and that the perimeter of the dots are soft/fuzzy. Remember that the fountain solution is a solvent. That softness is caused in part because of the fountain solution eating the edges of the dots - but doesn't affect the solidness (ink film thiskness). The slight edge softness is normal. The ink lay down across the solids is because the ink formulation for that press condition is good. Ink is designed to absorb/emulsify a few molecules of fountain solution.

Now compare those dots to those on the right:

]When over-emulsion occurs the fountain solution overcomes the ink resulting in one or more of these symptom: lighter dots (lower apparent dot gain), very soft and ill defined dot perimeters, and ink voids in the solids.

PS, their is usually no need to start your calibrations with linear plates.

 

[asr]

Before you do any curves you need to make sure that the press is printing properly, consistently, and repeatbly.

Hopefully you have one of these inexpensive microscopes so that you can view and photograph the dots on plate and in your presswork.

View attachment 293186

Look at the halftone dots on the plate. They'll look something like this:

View attachment 293187

The job of the press is to reproduce the dots on the plate on the press sheet. Properly done the result looks something like this:

View attachment 293188

Note that the dots are evenly dense across their surface and that the perimeter of the dots are soft/fuzzy. Remember that the fountain solution is a solvent. That softness is caused in part because of the fountain solution eating the edges of the dots - but doesn't affect the solidness (ink film thiskness). The slight edge softness is normal. The ink lay down across the solids is because the ink formulation for that press condition is good. Ink is designed to absorb/emulsify a few molecules of fountain solution.

Now compare those dots to those on the right:

View attachment 293189

]When over-emulsion occurs the fountain solution overcomes the ink resulting in one or more of these symptom: lighter dots (lower apparent dot gain), very soft and ill defined dot perimeters, and ink voids in the solids.

PS, their is usually no need to start your calibrations with linear plates.

thank you sir for this very informative inputs