using ink on inlay

I have some of the Grit Laskin engraving filler and realize that engraving fine detail is the preferred method. I'm wondering about using india ink or like inks to make the fine detail without engraving on the pearl. Does anyone here do it that way? I realize you couldn't do it on the fretboard but what about under lacquer?

I'd try it on some scrap to ensure a) the ink doesn't wick into any porosity in the pearl (being a natural material) and b) the lacquer doesn't cause the ink to bleed. If no issues I see no reason not to go for it in an area not subject to abrasion (e.g. the headstock).

Even if you could it would be painting and not engraving. I don't see the point of painting on shell. There are a few people who paint on instruments but it is not confused with inlay work by any stretch. Ink is soluable under lacquer anyway and it will bleed.
BTW, I'm not a big fan of grit's crayon. For filling in incised areas in shell, ivory, bone, etc, I prefer artist's alkyds. Buy the best brand you can to ensure the pigments are finely ground.