It's a good idea to let it slowly cool to room temp before putting it in the freezer! The slower the cooling, the larger and purer are the crystals. You can avoid the freezer altogether and grow large crystals by slow evaporation.
However, filtering is the wrong method here, it's not the way to separate fluids. Did you decant the naphta from the brown goo? Or did you just filter out dust, hairs etc?