I will start a new thread about this too, but I just want to post here because I think I may have found the underlying cause of at least part of what we have been discussing here.
I began with PiezoDN as a beta-tester couple months before the public release in 2016. I started out with the K6-Selenium inks in a 1430, and quickly was getting results way better than anything I had seen before with digital negs. Soon I swapped the Selenium inks for Carbon since that is my preferred tone for Piezo prints on paper, and found the Carbon to be just as good for negatives as Selenium in that printer.
Next, I set up one of my 3880s with K7-Carbon. Prints on paper were fabulous, but negatives had a grittiness in the denser end of the tonal scale (highlights on a print) that I had not seen before and couldn’t get rid of even after a year or more of trying various things that Walker and I thought could be the cause of the problem. I was leaning towards it just being a peculiarity of this particular 3880.
Last fall, as part of this and I think one other thread, we discussed the idea of swapping Selenium inks into the shade 2 and 3 positions since those are the inks the make up the bulk of the problematic part of the tonal range. I finally got inks and cartridges together and made the swap yesterday. The results are highly suggestive that the problem was caused by the Carbon inks, since after installing the Se shades 2 and 3 the problem is no longer there.
Here are pictures for your examination that show my results. Be sure to click them for a larger view, or download and examine them in Ps. I am including both the full targets and a detail of the top 4 rows.
Maybe this will put to rest the cause of this particular issue. I am very interested in hearing from others who have experienced this problem with Carbon inks in the 3880/P800 or any other printer. I suspect that a combination of minimum droplet size and maximum resolution is why I did not have this problem with the 1430. I’ll start a new thread for further discussion.