Picked this up as part of a set of 3 inks.  I actually wanted the red one, but the vendor had a bundle that made it worth getting 3, and since I was treating myself as a congratulations for finishing up a piece of writing I’d been working on for months, I was willing to splurge a bit extra and get them all.

Diamine Cool Green fountain pen ink with swatch, 2ml in a vial that I spilled on the table, and Kaweco Sport pen in “Marble Ocean”

I used this ink immediately after swatching it because I, uh, knocked over the full bottle on my table.  You can see the 2ml I rescued in the sample vial, and there’s a bit more in the pen since I was hesitant to put potentially messy or contaminated ink back in the original bottle.  (It spilled directly over a swatch of Diamine Red Dragon.  Though what’s in the pen doens’t seem to be slightly red or anything so clearly it wasn’t as big a deal as I thought it could be in the moment.)

I’m pretty pleased by how well it matches the pen, actually:

Diamine Cool Green wirting sample in my journal with Kaweco Sport pen, fine nib, “marble ocean” colour. Also a cool sticker.

Compared to the my current collection of teal-ish inks, it leans a bit more green.

A set of ink swatches to compare with Diamine Cool Green. Top three, left to right: Pilot Iroshizuku ku-jaku, Diamine Aurora Borealis, Colorverse Gyeongmyeble Yealdo. Bottom row: Jaques Herbin Emerald of Chivor, Diamine Cool Green, Teranshi Guitar Brilliant Mint.

In colour tone, I think it’s closest to Teranshi Guitar Brilliant Mint, but it’s much darker and a bit greener.  It’s also pretty similar to Aurora Borealis but again, more green.

I probably wouldn’t have bought this ink separately since I own full bottles of both Brilliant Mint and Aurora Borealis (the rest are unfinished samples) but it’s a really lovely colour and I’m not really sad to have it because I use a lot of greens to match stickers, and my love of plant stickers means there’s a lot of opportunities to use a subtly different green.  Plus it looks nice and behaves well in the Kaweco Sport and I specifically picked up that pen to be a work pen (that’s why the fine nib) so I’m excited to have a kind of matchy ink to go with it.  Though I kind of want one that’s more green/yellow and I definitely don’t have that in my collection!  Anyone found the perfect match for this pen yet?