Sailor - Jentle - BlueBlack
Sailor consistently makes reliable, high-quality inks. Their Jentle series Blue Black, often gets overlooked for Sei-boku, which is their pigmented Blue Black. The two are similar, but Sei-boku leans a bit more blue, while Jentle Blue Black leans slightly more grey.
Jentle Blue Black is a lovely, slightly muted, true blue black. It dries quickly, and it's well-behaved. It's a beautiful shading ink and produces a reddish-copper sheen in areas of pooling.
I often use this ink first in pens that I'm a bit worried about, as it's an easy ink to trust. If you’re looking for a nice, trustworthy blue black, and don’t want the additional benefits and concerns of a pigmented ink, Sailor Jentle Blue Black is a very affordable option, and although the Jentle series has been discontinued, it's still widely available.