Comment by michaelt
> many (most?) fountain pen inks are not waterproof.
I assumed this was for child friendliness - you just know kids are going to get ink on their fingers etc while changing cartridges from time to time.
> many (most?) fountain pen inks are not waterproof.
I assumed this was for child friendliness - you just know kids are going to get ink on their fingers etc while changing cartridges from time to time.
It could partly be that, but I've generally read that the default inks are not waterproof.
I was curious about this so I just did a quick non-scientific perusal of one fountain pen enthusiast shop's offerings. It shows 118 of the ink bottles they sell are water-resistant ink while 935 are not (looking at the Yes/No filter counts for "Water-resistant" at https://www.gouletpens.com/collections/bottled-ink). There's a lot of duplicate inks that can be purchased in multiple bottle sizes, but picking the three most represented bottle volumes (20ml, 30ml, and 50ml) it drops to 24 water-resistant inks and 578 inks that are not water-resistant.
The above includes a lot of "interesting" colors; further restricting to black ink only ends up with 3 that are water-resistant and 26 that are not.