I have previously posted that ink window on my Pel M100 has been stained after one round with Diamine Imperial Blue. I sent it out to Pelikan and when in returned, I saw no signs of cleaning. Of course, I didn't ask for it (I could, thinking about it now).

Anyway, I gave the Pel another fill with Imperial Blue and suddenly - all that is left from the previous staining is quite light purple tint to a previously grey ink window.

How the heck is this possible? Magic? Positive forces in my room? Beer breath?

I don't complain, of course.

Chemistry pure (clear) and simple the imperial blue just had the right solvent to remove the coloration, a slightly different ratio is all you needed.

Kurt

Well, it's the same ink, same bottle. The only thing that changed was that the Pelikans lubricated the piston, but that shouldn't have any effect.

Oh the magics of fountain pen world

It could be as simple as how well mixed the ink was when you loaded the pen.

If it was super-saturated on the first loading, the extra dye could easily come out of solution and cling to the pen innards.

Then later when you added a less saturated version (maybe you didn't shake the bottle this time?), the excess dye readily re-dissolved in the under saturated Imperial Blue. The dye was more attracted to solvation than it was to adsorption onto the ink window.

The piston lube tends to come down the window when you fill the pen. The ink stained the silicone lube and you second filling cleaned it off