guess the ink!

[BCDDiggler]

Noodler's Periwinkle

[migo984]

Pilot Blue?

Noodler's Periwinkle

Neither of these.
I haven't tried Noodler's Periwinkle; online pics look like it is slightly more violet than the mystery ink, but it seems similar with regards saturation.

[BCDDiggler]

Lamy Blue

[sgtstretch]

Kaweco Royal Blue?

[naimitsu]

J. Herbin Bleu Myosotis?

[migo984]

Lamy Blue

Kaweco Royal Blue?

J. Herbin Bleu Myosotis?

None of these. No one has guessed the brand yet.....

[BCDDiggler]

Pelikan Royal Blue

[migo984]

Pelikan Royal Blue

Not Pelikan Royal Blue .

[grainweevil]

I know you're not a fan, so this is a daft guess, but it reminds me of Iroshizuku Ajisai.

[migo984]

I know you're not a fan, so this is a daft guess, but it reminds me of Iroshizuku Ajisai.

I do have some Iroshizuku inks but this isn't one of them :-)

Clue 1: it isn't a Japanese ink.

[datainadequate]

Akkerman #4 Nassaus Blauw?

[migo984]

Akkerman #4 Nassaus Blauw?

It isn't an Akkerman ink, but Nassaus is indeed very similar & a good guess

[datainadequate]

De Atramentis Sapphire Blue?

[migo984]

De Atramentis Sapphire Blue?

No, it's not a De Atramentis ink.

[Wile E Coyote]

It's not PRDCSSB

Pilot Pigment Blue

[migo984]

It's not PRDCSSB

Pilot Pigment Blue

You're absolutely correct!...................it's not PTRDCSSB

Also not Pilot Pigment Blue I'm afraid. (It isn't Japanese).

[AzJon]

Montblanc Royal Blue?

[migo984]

Montblanc Royal Blue?

It's not a Montblanc ink.

[VegHead]

Kada Kada light

[grainweevil]

Kada Kada light

Had to look that one up!

Akkerman #4 Nassaus Blauw?

It isn't an Akkerman ink, but Nassaus is indeed very similar & a good guess

Huh, that's thrown me a bit, I confess. In that case I shall fall back on the old reliable and guess - Diamine Sapphire Blue?