I fell in love with my Parker 51 after inking it with an old bottle of Parker Quink black. But since the ink is pretty old, it’s not purely black as it dries. I see that it tends to be a little brownish. So I set out to find a better black ink that’s relatively safe for vintage pens and I ended up with Diamine Onyx Black. I love this black ink. It tends to be wetter than Quink (in my experience, at least) and flows smoothly in my Parker 51, which has become my standard pen for black ink.