A swedish fountain pen retailer, Pennspecialisten (www.pennspecialisten.se), advices fountain pen users to avoid black inks since according to him these inks are permanent and leave residues in the pen. Any comments on that?

I can't read the original page without a translator program, but I'd say he's probably referring to carbon soot based inks or technical inks which have shellac in them. Both of these are permanent and will clog fountain pens.

Black inks designed for fountain pens from reputable names like Parker, Waterman, J Herbin, Noodler's, etc are perfectly safe.

It's nonsense.

Some blacks, of course. But some other colors also. For example, most people will recommend that you not use reds and purples because you will stain ink windows. Iron gall should also be avoided.

Thanks, I also figured that it would be strange if for example Parker's own black ink would damage their pens..

Oh My, now all that Black ink is going to ruin all the pens I've been using since 60 (the year, 1960)
I better start being careful.
Time for a black ink alert, after about 48 years of using the stuff?
I think not

Well, I got the "avoid black ink" advice from Lamy itself.

An Ebay purchased Lamy 2K was badly clotted by black ink. I dismantled the pen and soaked it for days. Lots of clotted black ink emerged but it still did not draw in ink.

I send it to Lamy for service and the pen came back as good as new but with the advice to avoid black ink.

I had problems with other pens, too.
Now I switched from mainly black to mainly blue. Only one pen is loaded with Quink black.
This reduced the problems with clotted pens remarkably.

I have to admit that black ink worked fine during school and university years when I used my favourite pen quite heavy. Ink had no chance to dry up in the pen. The problems started later and mainly with pens I did not use on a daily basis.

So there might be a shed of truth in what the guy said. Thanks Piembi.

Wow, a long term scientific test to rely on. Better tell Lamy.

"En reservoarpenna är byggd för att användas flitigt, En längre tids uppehåll resulterar gärna i att bläcket torkar i spets och bläckledare. Men det avhjälps enklast genom att skölja spetsen i lite rinnande ljummet vatten. Undvik helst svart bläck då detta är permanent och ger avlagringar i pennan. Vissa innehåller sot och andra partiklar som kan skada pennan och kraftigt försämra funktionen."

Full text: "A fountain pen is intended for regular use. A long period without use usually results in the ink drying in the nib and feed. This is most easily fixed by rinseing the nib in a little running water. Avoid preferably black ink as this is permanent and leaves deposits in the pen. Some contain soot and other partickles which kan harm the pen and seriously harm its performance."

Any ink which dries leaves a deposit. I think they have just been a bit impresise by mixing a warning against certain kinds of black inks with a text about how to unclog a dried nib.