I've been sorting out some of my drawing equipment and in the process uncovered the bottles of ink needed for two of my favourite drawing pens. One was a very small bottle of black Rotring ink for a marker pen I used to draw "Journey" below. I stood the pen up with its reservoir in the ink bottle but even after several hours the nib still wouldn't work, so I binned it (and the bottle).
Better results with the old bottle of Quink and the Osmiroid sketching pen. That's what I used for "Daily Star 3" below and it looks like it works really well. Hurrah. Looking forward to using it again.