Consecutive sheet density variation?

SteveSuffRIT

Well-known member
Attached is a document (14 pg PDF) showing raw data analysis (Excel) and initial results from a simple test recently performed at Erie Community College (Buffalo, NY) School of Visual Communications and Technology and Graphic Arts Printing.
It investigates the amount of solid black ink density varaiation on 425 consecutive press sheets on uncoated paper on a single color Ryobi 2800 duplicator (ABDick/Itek).
Steve Suffoletto
 

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gordo

Well-known member
Is what the arrow is pointing at in the bow the 100K you're measuring? 'Cause it doesn't look like 100K.
 

Erik Nikkanen

Well-known member
Attached is a document (14 pg PDF) showing raw data analysis (Excel) and initial results from a simple test recently performed at Erie Community College (Buffalo, NY) School of Visual Communications and Technology and Graphic Arts Printing.
It investigates the amount of solid black ink density varaiation on 425 consecutive press sheets on uncoated paper on a single color Ryobi 2800 duplicator (ABDick/Itek).
Steve Suffoletto
So what is your question? What is the point of this test?

The results are interesting but not surprising.

The real questions an educational institution should be asking are, what are the causes of the variation, what level of variation is actually required to ensure that there is no visual variation and finally, what are the required modifications to the process to obtain that level of variation?

Unfortunately, the educational institutions are not capable of asking these types of questions and I don't see that changing any time soon. Looking at data does not result in knowledge.
 

Alois Senefelder

Well-known member
Hello Steve,

I'm failing to understand your choice of Image on which to conduct.... Ink Density Variation. There are much better Images available which will give a better understanding of Inking Variation.

Also, I'm not surprised that you see variation when using a Ryobi Duplicator, with its inherent - Poor Inking/Dampening Roller Trains.


Regards, Alois
 

SteveSuffRIT

Well-known member
Thank you for feedback

Response to post #2
Yes, the arrow is pointing to the area measured for solid density. That photo is a RGB flatbed scan of a original water color painting. The CMYK plate file used 100% maximum GCR in Photoshop so students wouldn't have top worry about misregistration showing. That area is only 100% K, no other colors.

Response to post #3
The question is how much density variation was there in 425 consecutive sheets. The point of the test was for student to learn something about this process (collecting samples, making measurements, performing analysis, visualizing data with graphs). If we conclude there is a problem, then the cause would first have to be identified before it could be corrected. I agree "looking at the data doesn't result in knowledge" but at least the students are being inquisitive, having awareness, and questioning an observed result different than expected.

Response to post #4
The test occurred after a student complained about wild density fluctuations, so is post event. It was not designed to test inking for mechanical ghosting, starvation, rerolling, or fall-off across or around cylinder.
 

Erik Nikkanen

Well-known member
Thank you for feedback


Response to post #3
The question is how much density variation was there in 425 consecutive sheets. The point of the test was for student to learn something about this process (collecting samples, making measurements, performing analysis, visualizing data with graphs). If we conclude there is a problem, then the cause would first have to be identified before it could be corrected. I agree "looking at the data doesn't result in knowledge" but at least the students are being inquisitive, having awareness, and questioning an observed result different than expected.
What might be of interest to your students is to get a better idea of the physical changes that are happening that result in the measured density changes.

If you make an ink mileage curve for that ink and paper combination, you can investigate the changes in ink as a percent of volume or ink film, that are related to the density changes seen in that test. You might be surprised at the total range of ink film variation that that little press is providing for that specific print image.

As a side note, that little press could be modified to obtain much more consistent results. This would be a bit too ambitious for your students but it could be done.

Another thing that could be done is to have someone with some programming knowledge, write a simple press simulator. One of the guys in my group, in about 1991, wrote one using arrays to represent rollers. It took him less than two weeks to write. We tested a production press design, Chambon, and ran it with different conditions to represent transient densities and also variations caused by ghosting. We also ran a simulation on a single form roller concept, that had multiple rollers on its surface. Ghosting reduced greatly on this concept press.

That simple simulation program only looked at variations in the press direction, so no affects of oscillation were examined. That would have been much more complicated to program. But that simple simulation method was very helpful to get a picture of how the mass transport of ink can affect print variations. And the mileage curve was used to convert ink film values to densities.

Hope this was of interest.
 
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