1 cm " scumming like" in the lead

I agree that this is plausible. Even a higher pigmented ink on uncoated paper will never get the rich densities associated with coated papers without running into emulsification issue if lefts to run at high levels. Often these problems wind up coming from upper management who insist on running things at max densities. Black ink run on an uncoated bond stock for example, will need to run a bit on the grey side to be able to print cleanly over the course of any run exceeding about 1000 sheets. If you look at the way a PMS book is laid out you will find that many colors start out with the base color somewhere on the middle of the page. Going lighter than the base color winds up being nothing more than the addition of transparent white. Going darker that the base color winds up being the addition of varying amounts of black. If your printing on an uncoated stock, pick the PMS color a step darker that the specified color. You won't be able to do this on all colors but when you can you should take advantage of this. By doing so you can arrive at the desired color WITHOUT having to run so much on your rollers.

 

Dear mz,
Did you solve your problem?

 

Curious , did you figure it out ???
Roller settings on the black unit ??

 

thanks Bill, Turbotom1052, Travis, mantman And Asem
thanks all for your contribution, after long trials and assessment i found its the dampening mix, adjusted by HDs and the problem seems to disappear.
Good day