Chu-shu is a lovely dark grey ink that reminds me of Diamine Earl Grey, but it is slightly more saturated, smoother and more purple than the Diamine ink. It is less purple than Diamine Vivaldi from the music collection and on par with Sailor Kobe #10 Mikage Grey.
Chu-shu shades in the right pen and paper combo, and I observed some coppery-golden sheen when using wet nibs, especially my Sailor 21kt H-B one—I’m not crazy about the colour of the sheen, though. The ink flows well and doesn’t feel thin under the nibs and coats them well. I’ve seen no feathering, no bleedthrough and almost no ghosting on thinner paper with wet wide nibs.
The ink is readable in all my nibs, from my Sailor 1911L 21 kt H-EF to H-B. Writing with Chu-shu and reading back notes written with it is a joy. It has enough pop not to look like a graphite pencil. I like greys with red undertones, and this one tickles my fancy!