Green in Yellow ink fountain roller

SteveSuffRIT

Well-known member
Your ink is NOT being physically contaminated by any back-trapping. You are seeing an optical illusion. The ink in the fountain looks very yellow because it is very thick (mass-tone) and more opaque. The ink on the fountain ball roller looks green because it is much thinner and now more transparent, showing the dark black metal ball roller underneath it. Have you checked the hue error and grayness or hue angle (h') and chroma (C*) of the ink on the press sheet, which is what matters.
Steve Suffoletto
 
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curiosity

Well-known member
in the 2nd image, it looks to me that there is actually contamination from the cyan. The yellow ink is thick yet there are a few ripples of green, which appears to be contamination from cyan ink.
To be clear...I am not looking at the duct roller.
Are my eyes lying to me?
 

gordo

Well-known member
in the 2nd image, it looks to me that there is actually contamination from the cyan. The yellow ink is thick yet there are a few ripples of green, which appears to be contamination from cyan ink.
To be clear...I am not looking at the duct roller.
Are my eyes lying to me?
Could be a reflection.
 

curiosity

Well-known member
I saw something very similar but way worse from a web press at a commercial printer in L.A. several years ago.
The yellow fountain was grossly contaminated and both magenta and cyan. It was mixed with yellow in places along the edges of the fountain where the ink was drier or coagulated. These areas were green and orange! So when I saw these pics, which show way, way less contamination (?), I immediately remembered the aforementioned.

Soooo, I'm skeptical of the masstone vs undertone explanation. OP may have a serious issue.
 

Cornishpastythighs

Well-known member
Look up Backtrapping on Google and you will get lots of ideas on how to deal with this. Yours does not look as bad as some I have seen and a little bit of press maintenance and good wash up procedures may help reduce it a bit, it is a part of 'wet trapping' and sometimes its as good as it gets.
Ink tacks can affect it but remember the tack number on the tin is just a number and does not take into account of fountain solution mixed in the ink. You can try running less water in the cyan(increasing tack) and more water in the yellow(decreasing tack) but dont go overboard
 
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Alois Senefelder

Well-known member
Hello fellow Lithographers and the Sceptics amongst us!


"There are none so blind as those who will not see"


....... some doubt about the terms - Mass and Undertone of Printing Inks.

To the sceptics...... in the following two pictures of Yellow Ink Ducts, do you

see any "Contamination (Backtrapping)"


Regards, Alois
ink_on_press.jpg
kms-litho-services.jpg
kms-litho-services.jpg
 

curiosity

Well-known member
from what I can see in the pictures, maybe some in top image, but none in bottom two. But because I'm not there, and seeing it for myself, my confidence is maybe 50/50.
 

Alois Senefelder

Well-known member
Gentlemen and all the Sceptics

I shall continue to posit.........Ink Contamination.

A telltale sign that this is taking place is, -- Trace "Whirls" (Magenta) appear of the backtrapping ink shows at where the bulk

of the Ink (Yellow) in this case, meets the Duct Interface. Printing Sequence -KCMY

Regards, Alois
 

sornchai

Well-known member
Gentlemen and all the Sceptics

I shall continue to posit.........Ink Contamination.

A telltale sign that this is taking place is, -- Trace "Whirls" (Magenta) appear of the backtrapping ink shows at where the bulk

of the Ink (Yellow) in this case, meets the Duct Interface. Printing Sequence -KCMY

Regards, Alois
Dear Alois
May middle and bottom pictures be ink shade ? Please explain for me if you think be backtrapping .Thank you
 

Alois Senefelder

Well-known member
Hello sornchai,


Process Yellow Printing Inks are in the main produced from 1) Diarylide Pigments - Yellow 12)

2) Benzidine Pigments. Both have slight differences in "Masstone v Undertone "
 

robb

Active member
I have to think every offset pressman has run 4-color job with a massive rich deep blue with very little yellow being used-the yellow gets seriously greenish in fountain and rollers in a few thousand sheets. Sornchai, If you are getting only that teeny bit of cyan in your yellow, it will not hurt a thing. Two things can make it better, but not much:
*lower yellow tack
*less squeeze between yellow plate and blanket (but be careful); I didn't believe it either, but it works well.
If running a lot of work with large blue areas and little yellow, put the yellow down first or second.
 

turbotom1052

Well-known member
As mentioned, if your yellow was contaminating you would see it on the fountain edges. A little tip.... If your getting ink contamination from previously laid down colors your usually dealing with one of 3 issues. The first possibility would be that your ink (yellow in this case) is too strongly pigmented. When an ink is too strongly pigmented you wind up running it at a thinner film to arrive at the desired density. A thinner film of ink will have trouble avoiding back trapping issues where the earlier printed colors migrate from the wet ink on the sheet, up through the blanket and ultimately back to your ink fountain. The second issue would be that the yellow ink is too tacky and is pulling the ink off the sheet. Often this tackier ink film has a direct relation to the inks pigment load. As mentioned in reason 1 a heavily pigmented ink will usually be run at a thinner ink film to arrive at target densities. We all know that a thinner ink film will be tackier than a thicker ink film of the same product. In the event your ink is pigmented correctly for its set, than you may want to consider reducing its tack with ink tack reducer. If it is pigmented correctly relative the the set than I would say to try starting by adding about 20% transparent white to the yellow as a test. If the addition of transparent white solves your problem then you know its too strongly pigmented. Additionally I would say that you need to be sure to not close your ink fountain all the way down in zones where there are no images. All color bars need to be run at full density even if there is no image in line with it. You should also allow some ink to flow into zones outside of the sheets perimeter. This slight flow of ink will help to prevent ink migration into the fountain from previously printed colors.
 

9162

Member
one simple may might be to reduce the tack / flow of the yellow and look for any difference .[back trapping]
l agree with all those before especially with mass tone and film weights
 

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