Evaporation Of Solvent Prior To Freeze Precipitation 

When the solvent is pulled from the soup in step 9 of DpTek1, the concentration of dissovled Purity Flakes can vary greatly depending upon 

1. the amount of solvent actually used for the pull

2. the amount of Flakes that the solvent has managed to collect 

If the solvent is at a high concentration of dissolved Purity Flakes (or saturated) for freezing, then the formed crystals will tend to collect and adhere to the bottom of the dish which will make the later solvent pour-off and crystal collection much easier.  However, note that if impuritieswill also tend to collect at the bottom (often as a layer of goo underneath the crystals layer) and may be difficult to totally separate.   However, providing a true 20°C pull has been used, goo contamination will likely be negligible.

If the solvent is at a low concentration of Purity Flakes during freeze precipitation then the crystals will tend to form in-solution as floaters, which can be more difficult to collect, but will normally be totally separate from any goo layer that might have formed.

At present, the recommended procedure is to evaporate the solvent down to the point at where it's starting to become milky (i.e. Purity Flakes are beginning to precipitate out) to achieve a standard level of concentration which should produce non-floating crystals.  

Optionally, even more solvent can be evaporated and then heated gently (e.g. by placing the dish in a heat bath) to re-dissolve any formed crystals back into solution prior to freezing.  This tends to produce an even better adhesion of the crystals to the bottom of the dish