Manufacturers always say never to mix inks unless they’re selling you a range of mixable inks, yet I have never had a problem when refilling pens that weren’t 100% clean. What are the worst reactions you ever got from mixing inks on purpose or by accident?
Worst reaction, although less of a reaction than clogging, was with Diamine glitter ink.
Worked fine with B-M nibs, but not mixed and certainly not with smaller nibs. Had to flush that out thoroughly.