I used Seitz-Kreuznach Dark Orchid in a Kaweco Sport with broad and extra-fine nibs. To me, Dark Orchid looked at its best with the wider nib. It is saturated and legible enough to work with an extra-fine nib, but it would benefit from an extra-fine with more ink flow than mine.
I’m not sure if I would classify it as a slightly blue magenta or a very pink purple; it could fit in either category. It actually looks just a little more blue than Waterman Pink, which is a bright pure magenta. Here you can see it compared to the standard Waterman Purple, on the left, and Waterman Pink, on the right.
Either way, it’s a cheery color. It’s especially nice on cream or off-white paper, which accentuates the warm magenta tones.
Here it is bracketed by standard blue and black inks, which gives a nice idea of the color from a wet pen.
Dark Orchid had nice behavior. It’s fast drying. My cartridge was a little slow to start flowing with my dry extra-fine nib, but everything was perfect once it got going. Again a wetter nib would have been a better match. The ink does feather more than most Seitz-Kreuznach inks, but I still consider it usable on all but the worst paper.
It’s a low-maintenance purple or magenta ink, which is always nice to find. It’s easy to clean, but as a corollary there’s only a bit of water resistance. After contact with water, traces of Dark Orchid remained on Rhodia and on more absorbent, lower-quality paper.
Paper towel chromatography shows the bright pink dye that dominates the mixture.
Living outside the EU, I order Seitz-Kreuznach products from Seitz Global, which sells Seitz-Kreuznach ink in 100 ml glass bottles for $9.90 and in 20 ml glass bottles for $3.25. Short international cartridges are $2.19 for eight or $3.62 for 14. George Seitz kindly added this cartridge to an order I placed, so I could sample the ink, before they started selling the smaller bottles.