A bottle of Parker Quink Permanent Blue ink, manufactured in England in the 1970s. One of three I bought this year as a job-lot, after seeing this online. It seems to be the ink used by my favourite author JG B*ll@rd. I've used this recently in the Pilot M90 and it's still good, it dries out to a very respectable darkish blue with no purplue tinge.
I've since departed from the blue-ink policy in the M90 by filling it with Diamine Woodland Green. (See last post.)