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I agree with https://www.penboutique.com/blogs/blog/fun-with-water-resistant-inks that Sailor Sou-boku is a really nice pigmented and water-resistant ink. I've been using it daily for a couple of months now.
I switched to it for writing in my planner so that 1) I can use highlighters over entries without smearing, and 2) when my < 1 yro puppy licks my todo list, it doesn't smear/vanish.
Can confirm it passes both tests.
