[Mocook]

Hello all,

I still don't get the point of concentrating your sample when recrystallizing. In a two solvent system (room temp) I have two solvents (methylene chloride and methanol) sitting in a flask awaiting for CH2Cl2 to evaporate. Whats the point in having the compound containing solvent concentrated if it will concentrate itself as it evaporates? Is it just a time issue, the more concentrated the faster the crystals grow ? 

[discodermolide]

It is a time issue. In this case you need to get a supersaturated solution of your compound in methanol.
Once this state is reached it may start to nucleate, that is crystal will begin to grow around microscopic dust particles or the like, or even imperfections on the glass surface. All of this takes time. You can't rush a crystallisation. But once you get the compound crystalline it will always crystallise.
Good luck.