Hi @Silly Party Candidate, and welcome to FPN!
It might help people to give you better ink recommendations if you reveal what make/model of ‘vintage’ pen you have, and especially if you reveal what type of nib is on it (‘EF’? ‘OB’?).
But here’s one from me anyway 😉
If you are after a purple ink with some water resistance, I would recommend Rohrer & Klingner ‘Scabiosa’.
Its water-resistance comes from it being a (light-) iron-gall ink.
Some people are wary of iron-gall inks, but they were commonly in-use in the era of ‘vintage pens’, and so should not present any challenges to your pen, as long as you never let the ink dry-out in the pen, and remember to flush the pen with plain water every three months or so.
One corollary of Scabiosa being an iron-gall ink is that it tends to feel ‘dry’ under a lot of pens’ nibs but, if your ‘vintage’ pen has an ebonite feed, and writes ‘wet’, Scabiosa should be a good match for it.
That said, although R&K’s iron-gall blue-black ‘Salix’ works really nicely in my vintage Parker “51”s, I found that Scabiosa felt painfully ‘dry’ from my first “51”, so I actually had to dump the ink out of that pen.
Another consequence of the ink being iron-gall is that its colour changes as the iron-salts ‘cure’ on the page.
It dries to a dusky purple-grey colour. Nothing else looks quite like it. And it gives you really beautiful shading 😊
I recommend that you search through the…
…and search for reviews of Scabiosa (and also of any other ink that gets suggested to you here).
I recommend that you read several reviews of any ink, in order to get the best idea of its colour, its behaviour on different papers, from different nib-widths, and from different pens.
I wish you good luck, and hope that you have fun on your quest
Slàinte,
M.
P.S. I’d vote for you! 😉
Edit to add:
Another place to look for inks that you might like the look of is…
If you see an ink in that thread that piques your interest, look at reviews of it to find out whether its properties look like they’d suit you.
And of course you could always ask whether people have used that ink safely, happily, or with joy in [your pen] 🙂