TWSBI expanded into inks in mid-2019. Like other pen-makers’ non-boutique inks, TWSBI’s seem to stand firmly in a middle-ground, neither dry nor damp, not over-pigmented, and (I suspect without testing) somewhere toward the middle of the pH scale.
TWSBI’s initial offering of inks came in two different sizes, 18ml and 70ml glass bottles, and the latter is interesting not only for its contents. The threads of the bottle are compatible with the cap of the company’s Diamond 50 after-market bottle, one meant to have inks decanted into it from less conveniently arranged bottles. This cap is rigged with a special adapter, allowing the Diamond, Classic, and Precision pens to be attached to the bottle for the sort of no-mess filling that was all the rage in the 1950s and ’60s. Thus, TWSBI inks can get into at least some of their pens without the need to wipe the point and also without the need to transfer the into into a different bottle.
The large bottles are also sold with a little insert similar to that in the Sailor Jentle bottles, allowing easier fills when the volume of ink in the bottle gets low.
Sapphire Blue: This is the name according to TWSBI’s site, although the packaging just says “Blue” (it also says 藍, but that’s just the Chinese character for blue). It’s more or less the standard blue that most companies offer, sometimes as “Royal Blue”, and is probably as likely to fade over time as most of the others.
Blue Black: This appears to be the only one of the original group of TWSBI’s inks that is formulated to be water-resistant. It also has an uncommon scent, inclining towards a floral fragrance; this is not strong, and doesn’t survive drying, but some may not enjoy it. Like many modern blue-blacks, it inclines toward greyness.