Bottle and pricingBottle capacity: 80 ml / 2.7 oz
Price / ml: $0.16
Color and saturationDiamine Prussian Blue is, well, a blue ink. However, the saturation is so low that it can be easily mistaken for a grey. Essentially it's a very dull and subdued slate blue, which is just fine with me. You might not like it ink at first, or at all. It didn't "sing" to me the first couple of days I used it, but then it started to grow on me.
Prussian Blue's muted tone actually makes a lot of sense in a formal environment, such as an office. Is it the best ink for official documents? Perhaps not, based on how light it is. But for less official papers it's pretty good, and the color is not the only thing that helps.
So what exactly is "Prussian Blue"? Interestingly, it's one of the first modern pigments. Does the ink resemble its namesake? I would say yes, allowing for differences in saturation.
Below I tried to compare Prussian Blue with two other muted inks I tested in the past, Noodler's Polar Blue (forgive the mistake in the photo) and Private Reserve Invincible Aqua Blue, though the three aren't very similar.
ShadingYou might be forgiven to think that Diamine Prussian Blue doesn't shade. Light inks don't always feature a lot of variation and it's almost the case here. However, this ink does have a little bit of shading, probably made more discernible by the broad nib.
BleedthroughBeing a light-colored and de-saturated ink, Prussian Blue doesn't bleed, even on cheap paper.
Flow, lubrication, and smoothnessOne very pleasant trait that Diamine Prussian Blue manifests is how easily and smoothly it flows in the Kaweco. It doesn't gush, and it has a very measured flow, yet it's wet enough (around a 6.5-7/10) that it satisfies my requirements.
Drying timeOn cheap paper it dries almost instantly, but on Clairefontaine 90g (a thick, glossy, high quality paper) it is more stubborn and might require up to 30 seconds to dry completely with the broad nib.
Smearing when dryA resolute no!
Water resistanceColor me surprised, but Diamine Prussian Blue is more resistant to water than it lets on. No where is it advertised as being water resistant but my standard test by which I let water run on a sample for 30s - 1m clearly shows that the ink remains perfectly legible. Granted, the top layer has washed off but what remains is more than enough.
ConclusionWhile the slate-blue / blue-grey of Diamine Prussian Blue might not appeal to everyone, I would give it a try if I were looking for a more formal shade of blue. It could grow on you too. It's a very well-behaved ink which flows smoothly, has just enough shading to make it interesting, and on top of everything, plays well with water.
Here are the two samples on photocopy, and Clairefontaine 90g paper, respectively.