Diamond mining refers to the practice of precipitating THC-a or CBD crystals out of a concentrated solution and starts with a subzero LPG extraction, typically below -100C. The low temperature extraction is designed to reduce the extraction of the molecules longer than our C-22 targets.
While THC-a is a carboxylic acid in crystalline form, when decarboxylated to THC it doesn’t form crystals, so first rule is use fresh starting material still in carboxylic acid state.
Crystals form when the solution becomes super saturated and initiate at points of nucleation. The points of nucleation can be particles in solution or irregular spots on the container wall that dissipate energy faster than the areas around them.
Temperatures lower than -100C can be achieved using an isopropyl dry ice slurry in an open jacketed column, or LN2 in a closed column. The temperature of the LPG tank is also reduced and the temperature of the LPG itself may be further reduced at point of injection using a counterflow heat exchanger and LN2.
Below about -42C, even propane has no head pressure and none of the mixes will have head pressure at -100C, so some must be provided in the form of a hot vapor assist, or pressurized N2 to push about 10 volumes of it through the column. At low temperatures the process slows down and requires about three times as much solvent volume as at ambient temperatures.
Following extraction, the overall volume is reduced to a sludgy state and the remaining liquid poured into prechilled containers, typically a Diamond Miner or a canning jar. They are pre-chilled so that the liquid doesn’t boil when transferred to them and then they are capped to stop evaporation.
Canning jars work but are subject to breakage from impact or thermal shock and are limited to about one atmosphere internal pressure. Some techs call for pressurizing the container to reduce solvent evaporation into the head space, and thus slow down precipitation in an effort to grow fewer larger diamonds.
The ability of a solvent to hold a solute is among other things, a function of temperature. It will hold more solute in solution at higher temperatures, so to start the precipitation and increase the number of points of nucleation, the diamond mining containers can be held in a dry ice slurry for a couple of days.
After soaking in the dry ice slurry, the lids are removed and the solvent allowed to evaporate at ambient temperature to a viscous state, where additional points of nucleation can be created by adding THC-a or CBD crystals from previous runs.
Processes vary, but the longer a crystal has to grow, the larger it is, with rapidly grown crystals having a more sugary or sandy consistency. For this reason, if large crystals are your goal, agitation is bad because it breaks up already formed crystals, increasing the number of points of nucleation, thus forming more smaller crystals.
On the other hand agitation when in the initial stages of crystal formation will increase the number of nucleation points to get the process moving.
Another factor is temperature and according to @otsccprime in his *Only The Strong Sauce article on Future4200, 26-29C/80-85F seems to be a good temperature for growing crystals within two or three weeks, and 18C/65F a good temperature to grow large crystals over a period of months.
*Reference: Only The Strong sauce tek at: https://future4200.com/t/only-the-strong-sauce-tek/44
If crystal growth stops, it may be restarted by lowering the pressure in the headspace using a valve or by loosening the lid for a brief burp. That allows more solvent to evaporate into the headspace so as to again supersaturate the remaining solution.
After the crystals are formed, they may be separated from the remaining terpenes, by allowing the container to drain off the remaining liquid through a strainer or using a centrifuge.
Some of the liquid will remain behind coating the crystals, which is how I prefer mine, but some processes call for centrifuging the liquid away, and/or washing the remaining terpenes off using a non-polar solvent like Pentane.
As some of the best THC-a diamonds that I’ve sampled were made by Erich Berkovitch of Pharmex fame and fortune, I importuned him to share some of his thoughts and techniques with us, which follows as article 10.9.1 Diamond Mining, separating THCA and terpene fraction via evaporation crystallization.