Platinum Blue-Black is an undersung workhorse of an ink, and one I use a lot. Some feel that this ink isn't really a true blue-black, since it has a strong blue undertone to it, but it's nice-looking nonetheless. In the U.S., Platinum black and blue-black inks are best known for being the pack-in inks for Nakaya pens; each pen sold comes with 10 high-capacity cartridges . As I've mentioned before, when I first purchased my Nakaya, the blue-black cartridges were the only ink I used in the pen for quite some time.
This ink contains iron gall, which can be corrosive to metal parts in pens if the ink is left in there for long periods of time (i.e., months), so take care to use your pens and/or flush regularly. Iron gall, however, is what gives this ink its key properties, from its nice color and shading (pictured) to its performance on (most) cheap office papers without bleedthrough or feathering.
Thanks to Jetpens for providing me with this bottle for review. Platinum Blue-Black is available in 30ml and 60ml bottles, although it appears that Jetpens only stocks the 60ml bottle currently. (link here)
DISCLAIMER: I received this bottle free of charge for review purposes.