I recently bought a ~1940s Waterman that I absolutely love to write with. I've owned vintage pens before, so I was expecting a few quirks, but nothing major because of the previous owner's restoration.

After having a bit of flow trouble with colored inks, I switched over to the tried and true Serenity Blue which I have never had problems with in any pen. After about a day in the pen, the ink came out a super saturated blue-black, which I thought might just be a quirk of the pen's wetter flow. A day later, after flying for Thanksgiving, it stopped writing, which I blamed on forgetting to empty it before (it had leaked into the cap pretty badly).

When I got it home and flushed it, dark spots of particulate came out with each press of the lever, each of them slowly seeping blue into the water around it. I refilled the pen, and a day later it stopped flowing again. It's clear the ink is drying out or gunking up in the pen, but I'm unsure how or why.

Is there an easy fix? I have some wetter inks like Pilot Blue-Black on hand, but I'm honestly scared putting them in a lever-filler while not knowing the pH.