I know waterproof inks can be a little controversial in the fountain pen community because some can be hard to clean out, and some of the smaller brands can make some waterproof inks that are not always consistent. However, I have had pretty good luck with the DeAtramentis document inks. I haven’t tried mixing them, which you can do, and there are some websites that explain how to do it. I wanted to share some info about my experience with DeAtramentis and how these document inks can behave a little differently, depending on the nib. If you don’t want to read my chicken scratch, my point is to try your ink in different pens with different nib sizes.
Sometimes people want to buy an ink and match it to their pen exactly or at least have the pen and ink have the same base color. It’s possible that the ink may not behave as anticipated in that pen that you thought the ink would be the perfect match for. I used to like to put this document fuchsia ink in a TWSBI 580 because the color reminded me of a fabulous magenta nail polish. And wouldn’t it be cool to look at that rich magenta through the demonstrator barrel? But the TWSBI wasn’t having it. The DeAtramentis document fuchsia would often clog. Yet that same ink in a Franklin-Christoph Model 02 does great. Similarly, the document turquoise does well in the Lamy Lx pictured below.
People who are newer to fountain pens might not play around with the inks in different pens as much or might not know to try a drier or better flowing nib. So if you have a fussy ink, waterproof or not, try it in a different pen before tossing it or giving it away. You probably will still be able to use it.