I've found this to be a great ink, it has a nice color that ranges from blue-gray slate color to deep near-black. It seems quite resistant to bleedthrough, even on fairly thin paper within reason.
LAMY T52 Blue Black 50ml Ink Bottle
Love the stuff. Love the service
Good color —quality ink. Recommended by seller. Excellent product and outstanding service.
I have not used any out of the bottle yet, but I did use the LAMY blue in the cartridge that came with the pen. Writes very well and the packaging on the bottle is very well done. It even comes with a little dispenser for wiping cloth!