If you have any large particles, they take forever to react if you aren't using a stirrer. They do eventually react, on the order of months. If it doesn't seem to be getting any darker, it's probably done enough to use, even if there are some particles left in the bottom. Just draw some off the top if you want to start using it. The lower concentrations just don't look very dark when you aren't looking through a lot of material. In a tablespoon measure, for example, mine looks kind of whiskey-colored. If I look through a clear glass 750ml bottle of it with a bright light behind it, it has the characteristic deep magenta-red color.
You mentioned that you only got 300mg back out of the porcelain mortar. Did you use less oil with it, or was the idea to try to react it out of the mortar using olive oil, and make 750ml of a hopefully close to 500mg amount? My experience was similar, with getting the shiny metallic smear in a porcelain mortar. After scraping, I ground with some olive oil, but I don't know how much I ended up with. Next time I'll probably crush it on a sheet of glass using something very non-porous, then scrape it up with a razor blade. My first half gram batch wasn't ground at all; I just dumped it in the oil. It was going nowhere after a few weeks of daily shaking, so I ground the other half gram and made another batch. It reacted in short order, but I don't think I worried if there were a few particles on the bottom. The first batch has just been sitting on a shelf, undisturbed for 5 or 6 months now. I looked at it recently, and it looks like it's done now. So I guess if you wait looooong enough, the big crystals will eventually dissolve.
The particles shouldn't be very big. Both batches were crushed, one of them
very finely in the mortar, but I see no obvious difference in reaction rate.
The bottle with the finely crushed 300mg contains roughly 450mls of olive oil; the remaining 300mls are in the mortar, so the C60/OO ratio is roughly the same everywhere, and we do hope to eventually pour the mortar-oil into the mortar-bottle for a complete-ish batch
Both of my bottles sound similar to your finished one color wise - it's not quite magenta, but a pretty sound red if you look through the whole bottle against a white light - but the remaining C60 is definitely more than a little residue.
I'm not sure what to make of it. From your descriptions, the reaction of fine C60 should've been a bit quicker than this. Unreacted OO probably hasn't run out, potential things dissolved in my brand of olive oil shouldn't even matter if we're talking reaction rather than dissolution (I think?)... is it a reversible reaction, the balance of which might shift under different conditions?
Anyway, I've got two options; add more oil or wait longer. Either will probably work out, so I'm still optimistic. =)