By the way, do you know the Spanish company FPNibs.com? They have a "keyhole" nib that opens up remarkably, but they use a plastic feed that rquires writing a bit more slowly to get full advantage. Not a bad thing, really, for people like me, who tend to write too quickly. I believe they use Jowo 6 nibs as their starting point (as did Richard Binder when he was creating high-flex nib units for Edison pens).
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www.newpentrace.net