When researching, it happens again and again: You run into a dead end, or something that feels like a dead end. That can be due to so many reasons - there's little or no literature about it, you have found about everything there is, or the literature is all really dated, or the topic has only been looked at from angles that don't help for your own project.
And regardless of when you start and how long you planned to research, there will be a point where you are going to stop, or have to stop. Because you run out of time, or out of energy, or both. Because at one point, everything needs to be finished, or it will start to drag you down. Obviously, that cutoff point is coming faster when you are starting with little leeway in regard to time or energy... and I hate it. I don't like to stop, so it can be really hard for me to draw that line and say "no more". Yet that is essential - it's the art of hitting that sweet spot between getting everything you can while still not wasting too much time. You get a similar phenomenon in a lot of design work, where the last 5% of the work tend to eat up 95% of the time. And I've had it time and again that a jackpot turned up when I had already inwardly scolded myself for still going on though it was clear that nothing more would turn up. That's not making it easier to stop.
It's also not made easier by the fact that these searches usually turn up more interesting stuff from the sidelines. Like this article about how tannin and iron dyes eat up fibres. Or this one about identifying dyestuff (unfortunately behind a paywall).
Or the complete original Plictho by Rosetti. Now if only my old Italian were better...
(I'm looking for the bit in the Plictho where lead is mentioned in regard to dyeing textiles. Anyone have that thing handy?)