Diamine Herbert is part of the iridescink series exclusive to Cult Pens. It is called Herbert for the 80ml bottles and Herbie for the smaller 30ml bottles. This is a dark blue ink with a red sheen. The ink has an average flow.
On Muji Planting Tree paper, there is little shading, no sheen, some feathering and a tiny bit of bleedthrough.
This was written with a TWSBI ECO-T medium nib.
Below are a couple of photos of how it looks when it was written on both sides of the paper.
Disclaimer: This ink was purchased by me and all opinions/photos are my own. This post was not sponsored.