This is Octopus Fluids' Sea Serpent (indigo blue with copper sheen) fountain pen ink, which has a stunning multi-color sheening effect.
Where it fits in:
Octopus fluids is an underrated German ink maker, and I adore their inks — this sheening line is just as striking as the most famous sheening inks currently available in the US (think: Diamine’s much-loved Polar Glow).
