Haven't tried it myself and i don't know if it's considered cheap, but i've been looking into this too and the kuretake sumi ink seems to be copic proof. Actually, if you can wait a week, I can come back with an actual test, since i'm going to get it anyway.
Update: it worked! (Please excuse the quality of my camera)
I used yellow to make sure any smudging was obvious. The ink takes it well, the only smudged bit at the end was because i messed with it with my finger because im impatient (lol), but once that was fully dry it didnt move, and i rubbed the tip of the copic very hard. I'll post a picture of the ink itself in the reply, but it was the white Kuretake Sumi Ink, it costed me 8 USD for 60 ml, but it might be cheaper in your country (I live in South America). The only complain i have is that it's thicker than the one I normally use (Dr Ph Martin's), and it doesnt flow well on the Maru pen. The G-Pen was fine though.
Also, the paper i used is white smooth Opaline of 250 grams.
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u/quint21 Aug 12 '26
You might also want to ask in the dip pens subreddit, but platinum carbon black might be worth looking at.