Being happy, but perhaps a bit foolish, in buying over a liter of Pilot ink in the 350mL bottles: I thought I'd see if the mixes would make for anything more interesting: And I'm happy to say, since I like purple and burgundy, the experiment is a success. For non-printer people, K=Black ink. All the combinations work. I made up small vials of the dusky purple 2:1 Red:Black and the mostly Red with some Blue-Black (maybe 8:1). I'll let the vials sit for a while before trusting the mixes in fancy pens, but no immediate issues. Edit: That BB+K must have had some red in it. Here's some mixes of those two uncontaminated: