I know a bit about fountain pens and how to repair them but I’m utterly ignorant about ink. I am often asked which inks to use in sac fillers. I usually reply to the effect that I use Waterman or Quink when testing the pens I repair. I advise against using heavily saturated inks in sac fillers because they can be difficult to flush. Baystate Blue, lovely though it is, is an absolute no-no.
Beyond those few simple guidelines I am woefully ignorant. I do have a wide variety of colourful inks but I use them in converter fillers. I know nothing about their suitability for use in sac fillers.
One piece of advice that I am confident about is that sac fillers, especially lever fillers, are not the pens to use if you want to change colours often. It takes a lot of cranking of the lever to fully flush such a pen and doing that too often will stress it and may lead to damage. Button fillers are a little better but not ideal for that purpose either.
After all, back when our Conway Stewarts and Swans were in everyday use most people, whether at work or at home, would have one bottle of ink that they repeatedly refilled from. They would only flush the pen when the ink flow began to be affected. With a large daily throughput of ink that would not happen often.
What are your thoughts on the matter? Are you very careful and only use Waterman Mysterious Blue in your sac-fillers or do you just fill the pen with whatever comes to hand and never mind the consequences?