Just like the other dark turquoise inks in my list, Ku-jaku also shades beautifully. Shading is a big factor for all of my favorite inks, and the subtle changes that I see in Ku-jaku are marvelous. The light end of the spectrum is a medium, electric green that deepens into a dark blue-green that reminds me of the sea. If you're a fan of shading, this ink will not let you down.
When it comes to dry times, Ku-jaku is pretty fast. In my tests, the ink was dry by 20 seconds, but pretty much smudge-proof by about 12-15 seconds. Only a very deliberate and heavy rub would smudge the ink after about 12 seconds. This is a great drying time and something to consider if fast drying inks are important to you.
Feathering is non-existent if you're using decent paper, and show-through is minimal. Really, every aspect of this ink is on-par with all of the Iroshizuku offerings.
Of course, you can pick this up in a 15ml bottle or a larger 50ml bottle. I opted for the smaller bottle on my first time around, but I'll definitely go for the larger one when it's time to replenish my stock. So far, this ink has been going fast due to the popularity.
It's an Iroshizuku, so you know it will behave well. All that's left to consider is the color. Turquoise fans will love it, but it might have limited value if you already own some of the comparable inks mentioned here. Still, it's unique enough to merit space on my shelf!
(JetPens provided this product at no charge to The Pen Addict for review purposes.)