Hi Noelle, the best ink I know for this technique is “Pelican Fount india” , don’t be put off by the india part of the name ! It isn’t shellac based & is safe in fountain pens.Well not as safe as the normal dyes -don’t let it dry out in a pen but I have used it for decades for this technique without problems.
It has the same carbon nano particles that you are familiar with in the platinum carbon & similar inks.
It is best to take your wash off the lines the same day you draw them but you don’t have to.
Otherwise it behaves perfectly for this technique.
Another equally good ink for this technique is “Higgings Eternal ink” again it can be used through a fountain pen however after a couple of days the feed starts to slow down a bit ! – So I reserve this one for a cheaper disposable fountain pen & keep it washed out.
I do have a couple of very expensive fountain pens that I personally just can’t bring myself to fill with either of these inks – Just in case despite the reassurances of both of these manufacturers that they are fine in fountain pens.
It is though the nature of ALL pigment inks that they are a bit dodgy BUT they do wash to a nice even grey wash without the purples & greens that you so commonly found in dye inks.
The best light resistance of any dye ink by far (which still doesn’t come close to ANY carbon ink’s light resistance) is “Pelikan 4001 “Black only That ink washes well , lasts very well for a dye ink, & can safely be put into any pen without any fears.
I know all this as a result of my own light fading tests done over 10 months in a south facing window in a very sunny year ! & repeated twice over the years.
Cheers Mike

Higgins Fountain Pen India is another cheapie you might research. It also claims to contain some tiny carbon pigments. I’ve never done a test for light-fastness with it but it dries waterproof and I haven’t had issues with clogging in my refilled Varsity “disposables” or my Platinum Preppy (very inexpensive pens and very inexpensive ink). Higgins FPI cost slightly less than 5.00 USD last time I bought a bottle. Might be worth looking at some reviews.

Thanks for the info, Lamar!

No problem, but I looked at my bottle and did a little research and saw that it doesn’t claim to be waterproof, as I incorrectly stated It does dry to a strong water-resistance, though. Higgins lists it as pigment *and* dye-based. And I’ve never seen such mixed reviews! It works great in my cheapo fountain pens, but it might not be what you’re looking for since it does contain dye and is pretty permanent if you allow it to thoroughly dry.

Online prices are high in many cases. I wouldn’t pay more than 6 dollars for it.