For me, those swabs are as plum as Grey Plum ever looked when dry.
I used KWZ Grey Plum in a Kaweco Classic Sport, with both a medium architect’s nib and a fine nib. With that pen, on almost every paper, KWZ Grey Plum displayed its plum tint mostly when wet. It dried down to a color that varied from dark grey (on more absorbent paper) to light black (on more fountain-pen friendly paper).
Perhaps in a very dry writing pen it might look more plum. And I did find one or two very low-quality papers that made Grey Plum looked more plum. But with this pen, on fountain-pen friendly paper, I ended up classifying KWZ Grey Plum as basically an “almost black” ink.
Here’s a writing sample showing how Grey Plum looked for me on Rhodia.
That “almost black” quality makes KWZ Grey Plum a good choice for a stealth black ink, one that would pass as a standard black but still look slightly distinctive.
It’s a very legible ink. Here’s a writing sample on cream-colored Tomoe River paper.
And performance on poor paper is good, with a good resistance to feathering. Here’s a writing sample on my normal paper, Staples Sustainable Earth legal pad paper.
You’ll note that on this paper, which is the most absorbent of the papers I that regularly use and have photographed, Grey Plum looks a tad plummier.
Grey Plum is a nicely wet and nicely lubricated ink, but it dried quickly on the page. It cleaned up incredibly easily even after weeks in the pen, with just a few flushes of water.
This is not a water-resistant ink. Regular paper will absorb enough dye that a remnant remains after the purple dye initially washes away, but on fountain-pen friendly paper nothing is absorbed, and the writing all washes away.
Fun fact: Grey Pum’s purple dye becomes most noticeable when the ink comes into contact with water, either when you’re cleaning the ink out of the pen, or when water gets on a writing sample. Water lifts and liberates the purple.
The purple tint is also fairly apparent on swabs. In fact, if one were just comparing swabs, KWZ Grey Plum would not look particularly black or grey. Not even when compared to unusual and lighter black inks.
If one were just comparing swabs, KWZ Grey Plum would look like a rather conventional, but attractive, grayed-down, blue-tinted purple.
So it’s interesting how much darker and grayer KWZ Grey Plum looked for me when I actually wrote with it in my pen.
The closest ink to KWZ Grey Plum that I’ve ever used myself is Diamine Eclipse. Except I don’t like Diamine Eclipse, at all. I find Grey Plum much more pleasant and attractive, personally, because it’s lighter and has more shading. Combine that with its excellent behavior in the pen, and easy-to-clean nature, and I can see why Grey Plum is popular.