The sac problem is certainly due to a harsher ink, no doubt. A lot of the modern "boutique" ink makers aren't really considering vintage filling systems, unfortunately. I have no problems with any ink in our converter pens, but I have had to warn people out some inks with our pens that use latex. I started getting about one of these issues a month, and now I am getting about 2-4 of these a month.
Inks that he recommends include: Waterman, Sailor, Aurora and Diamine. As luck would have it, I currently have no ink from any of those companies! (I've had Waterman and Diamine in the past, though. I didn't ask about Herbin, perhaps I should?)
He also pointed out this article from Richard Binder: http://www.richardspens.com/?care=inks
So... Where does this leave me? Do I give up all my favorite "boutique" inks and permanent inks and switch everything out for old-fashioned weak-and-washable colors? Or do I get rid of all my pens with rubber sacs and bulbs?
OK, let's calm down. I'm not getting rid of all my vintage pens, that's for sure. However, I don't write with them all that much on a daily basis anyhow. I'm using mostly modern pens these days. So... I doubt I'll be buying any more modern pens that use rubber sacs or bulbs. There are plenty of other ways to fill a pen. Now I just need to pick out a rubber-friendly ink or two for those vintage pens, I guess. It's an excuse to buy more ink!
Edited by tonybelding, 15 June 2014 - 01:44.