I recently test dipped a number of grey/gray and black inks for comparison.  The paper is Rhodia notebook graph.  Of particular interest is the relative blackness, if you will, of the Noodler’s Heart of Darkness (HoD) ink.

In my own opinion, Aurora black (which has been my favourite until now) is a worthy competitor; however, Noodler’s HoD is the black ink that I prefer.