I finally remembered to fill and test my Kakimori Frost rollerball which takes fountain pen ink. I filled it with Diamine Sapphire Blue. It's a bit different in that you fill the converter while it's disconnected and then press it on, rather than drawing ink up through the tip.
Writes very well, it's very smooth so far, but also puts out fairly wide lines. It's supposed to be 0.5mm but feels a bit wider than that in practice. Looks great, though.
Questions or comments? Contact me on Mastodon