You would think all black gel ink made by one company, under the same brand, would be the same throughout the product line, but they're not. If you look at the first four pens tested (upper right) you'll see they're all Uniball. The second pen down turned out to be a favorite as the bleeding was minimal and the ink has a slight blue (cool) cast. As I tested Kohr-I-Noor, Gelly Rollers, Pentel, Faber Castell, Pilot, Yafa, Foray, Papermate, Pilot, Itoya and a bunch of no-name black ink pens, I found the same variations in ink and the amount of bleed I got.
By testing out my materials BEFORE I'm on location again, I will (hopefully) eliminate anymore (unpleasant) surprises and may even be able to use the info to my advantage. Say if I want a pen that really bleeds, I would choose one of the Pilots. If I want just a little bit of bleeding, I would wait until the ink was drier, regardless of the pen I was using.
* To test the pens, I wrote the name of the pen on wc paper, then a scribble, some dots and a line or lines. I then immediately washed over the scribbles, dots, and lines with clear water. After the writing had an opportunity to dry (about 30 minutes) I washed over the names to see if they would bleed. The majority of the inks, once thoroughly dry, bled very little.