They look nice.
So the whole solution that contained your solute and your choice/s of solvent completely crystallised in 1 day, or are these crystals taken out before the whole crystallisation had finished?
We also take around a day, but we have increased this to 36 hours and currently obtain...
Build up of pressure if you seal completely, I would recommend having slightly ajar to prevent build up of pressure and also to contain any fumes / smells, of course extraction of some sort is recommended. I'm comfortable using a temperature between 38°C to 40°C when performing a 4MMC synthesis...
I think 300ml DCM is plenty for this amount of BK4, 500ml in my opinion is too much and you could be saving money instead.
How long does your crystallisation take out of curiosity?
Hope you're well.