From Marsofolds Tek:
"Naphtha : the freeze-precipitation technique is a double-edged sword. Very convenient and high quality, but highly dependent upon knowing the approximate amount of DMT expected to be precipitated.
If you use too much naptha, then only a little bit precipitates out. If you use too little, then it doesn't extract it all out of solution. It is the simplest case of recrystalization. The best way using it if you aren't very sure of the yield is to use a slight excess to extract, then evaporate it down to 10% of the original volume. THEN freeze it.
This will pretty much guarantee excellent results. For example: For a pound of rootbark use 500 milliliters of naptha to extract. Then evaporate it down to 50 milliliters. Then freeze it and filter out the crystals.
By the way, you must very quickly filter it within a minute or two after removal from the freezer so it doesn't have any time to warm up. And your freezer can't be marginally cold. If it doesn't freeze ice cream HARD,then it isn't cold enough. -20C is about where it should be."

This finally clicked in my mind. The reason for so many low yield extractions during the re/x phase , was because I had too high a ratio of Naptha to DMT in solution, so it would not precipitate out during the freeze phase. Reducing the volume of Naptha by evaporation to 10% of the extraction volume prior to freeze precipitation will optimize the yield.

Took me a while to finally understand the value of this critical step!!!

DP

Not sure if you mean too much naphtha during extraction or during recrystallization. If you mean that you used too much naphtha during recrystallization, then you are not doing it right. When done properly, it should not require evaporation.

Only use the minimum amount of warm solvent that is needed to dissolve almost all of the dmt in it. Keep the jar in a warm water bath while dissolving the dmt and when after repeated stirring, a few crumbs of dmt remain at the bottom, you know that the solvent has been saturated. Decant the still warm solution from any impurities that were insoluble in the naphtha into a clean and dry container for freeze precipitation.

Slow crystalliztion, by slower cooling improves the results. Letting the container and the saturated solution cool down to room temperature before putting it in the freezer will give bigger crystals. Intermediate placement in the refrigerator also improves results.

Do not heat the solvent too much. It must be warm of course, but not over the melting point of dmt. If it does, dmt will initially start precipitating in molten form when the solution cools a little, but is still hot enough for dmt to exist in molten form. This molten dmt will form blobs as they solidify, not nice crystals.