@vfrmedia thanks for checking that, but this one is in the "dokumentenecht" section, it says that it doesn't wash out, but I need it to be really waterproof, which is a different thing.

I don't need the writing to be preserved, I want the ink lines to look good after applying watercolours.

maybe I should use my india ink with a dip pen. It's bit messier
to carry around, though.