Update May 2023: Added more sketches and tests.
Winsor & Newton produces two black inks: Black Indian Ink and Liquid Indian Ink.
The Liquid Indian Ink is actually sumi ink, ink that's ground with water from traditional Chinese stick ink. The ink is heavily pigmented and is not meant to be used in fountain pens.
If you add water to the ink and leave that undisturbed for some time, you can see the pigments sink to the bottom.
Sumi ink is meant for calligraphy and lettering work because there's variation in the light and dark intensity within strokes.
The ink is available in small 14ml and 30 ml bottles. The 14ml bottle is really quite small.
Here are some tests.
The ink flow is good and it dries fast.
When the ink is applied, you'll see lots of particles. It's heavily pigmented and you're recommended to wash your brush or dip pens after use.
As you can see the pigments are not evenly spread out.
It can hold a sharp edge well.
The ink is not waterproof but is quite water resistant. Once dried, the ink does not smudge and hence can be used in sketchbooks where pages touch each other.
I like to use Sumi ink as ink washes for my sketches.
The selling point is the beautiful granulation and texture sumi ink can create. If you like ink that looks flat, go with the normal Indian ink. How the granulation looks will depend very much on the paper texture.
And if you want to use sumi ink like watercolour, it's best to use good quality watercolour paper that can help you create wet-on-wet techniques more easily.
To create gradation with sumi ink, you have to use more water because the ink is kinda thick. And if you use too much water (right side), the pigments will move to the bottom if the paper is tilted at an angle.
Sumi ink dilutes quite well without any change in colour temperature.
If you have a waterbrush, you can have a rather compact sketching sketch with just the small ink bottle, waterbrush and sketchbook.
The difference between sumi ink and watersoluble graphite is concentrated graphite is not as dark compared to sumi ink.
Sumi ink may be made for calligraphy and lettering use, but I like to use it for pen, ink and watercolour sketches. Sumi ink is affordable and fun to use.
Winsor & Newton's version of sumi has more texture and granulation compared to the Kuretake Zig Cartoonist Sumi Ink 60.
If you want to learn more about using sumi ink for sketches, check out my online art course on Skillshare. Or check out these two timelapse tutorials on Youtube featuring sumi ink: