My Parker 45.
A while back Elwood Smith posted a great article where he shared his wisdom on fountain pens and ink that is permanent and appropriate for use in fountain pens. You can find his informative article by clicking here
On Vern Mercado's recommendation I am using another ink that is truly permanent, and works like a charm. It has the richness of sumi ink, and hasn't clogged my Parker 45. It is available in 50 something colors. After it dries on paper, it is there to stay. No bleeding. I have tested it on both quality (N.Y. Central 100% rag) sketchbook paper and Strathmore 500 series board.
This wonderful ink is made by NOODLERS Ink, and you can check out their informative, yet not too well designed website by clicking