This week I decided to try a new ink in my TWSBI, so I chose Pilot Iroshizuku Tsuki-yo (Moonlight) since it's darkish, blue-black nature would be appropriate for office and otherwise. I used this ink daily, throughout the week, and was happy with its overall performance, but, in the end, I'm not entirely crazy about the color.
In particular, I have been most curious about this dark green/blue/black "family" of inks, and decided to include some swabs of Diamine Twilight and Rohrer & Klingner Verdigris. All three inks are new to me, and Tsuki-yo is the only one of the three that I've used extensively up until this point. I had imagined these three to appear so similar as to be almost indistinguishable. But that's not the case at all. I was surprised at the results of the swab test: compared to Twilight and Verdigris, Tsuki-yo almost comes across like a dark turquoise. To my eye, at least.
Tsuki-yo performed admirably for me this week, including on cheap Staples legal pads that we use at work. However, I won't be rushing to buy a bottle of this one since I much prefer a darker blue-black.
Interestingly, the R&K Verdigris went down on the paper a very greenish, blue-black but dried a dark blue with a slight violet undertone to it. Of the three, Twilight strikes my fancy because it reflects a nice balance of dark blue-black with only a slight hint of green, and also has a bit of sheen to it. Ironically, while Diamine Twilight is named after the evening sky, it really reminds me of ocean waters.

