Good point, I will try a cartridge. Thank you!
If surface tension is the problem, how do I fix the issue? I was thinking of putting a tiny bead, which is present in many cartridges, into the Sheaffer converter, but the converter is very difficult or impossible to disassemble without damage.
The first thing to try is surfactants; flush the converter with water that has one drop of detergent added. If it still forms a bubble and does not flow freely use a wood toothpick. Dip the toothpick in detergent and wipe it off then insert the toothpick in the ink through the opening in the converter. Just dip it in, pull it out and throw it away. If that does not work get a small light compression spring. The ones used on computer keyboards are about right. Thread that in through the hole. It will be heavy enough to move up and down and so break up a bubble and soft enough to compress when you fill or empty the converter.