There are two processes that can produce emeralds, generally known as Flux Growth and Hydrothermal Solution. Both processes are time consuming and costly for synthetic gems, with emeralds typically being the most expensive synthetics due to the requirement of expensive equipment and long periods of time for crystal growth. It is not unusual for a year being needed to form the emeralds, and more time is necessary to form larger crystals.
Flux Grown Emeralds
As per the title, the Flux Growth method uses flux. This stuff is meant to dissolve other elements at refractory-grade temperatures. Think hundreds of degrees Celcius, though the exact temperature for formation differs between gems.
Additional adjustments to the temperature may be made over the course of an emerald’s formation, though the exact details vary between the different labs that create synthetic emeralds much like a recipe. These specific details are not publicly disclosed.
In terms of crystal formation, uncut flux grown emeralds appear more like natural emeralds. This is due to the fact that they spontaneously nucleate, or the emerald crystal starts to grow from nothing but the flux solution. You can tell the emeralds below are synthetic because the base of the specimen is emerald too, not quartz, calcite, or schist, some of the stuff emeralds naturally grow on.
The Hydrothermal Process imitates not only the temperature conditions that flux grown emeralds form in, but the pressure exerted under the surface too. This means a whole other set of controlled values for the crystal formation and different emerald “recipes”. All of these are completely different from flux-grown methods, since flux is absent from the process.
Hydrothermal emeralds are grown from a seed plate, which is colorless beryl. Since there is a specific growth direction away from the seed plate, there are often inclusions visibly growing in the same direction that look like nail heads and/or chevron patterns.
Between these two processes, there are unique inclusions and growth features specific to them but these features are not always obvious. There are also similarities between the two processes since both require long periods of time for emerald formation, and the emerald crystal’s form is not 100% controlled.
While the temperature and/or pressure may be controlled, the exact formation of the emeralds inside the crucible is unknown until formation is over. A lot of the rough emeralds are cut away to make a high-transparency emerald, sometimes with as much as 80% of the original material being removed. Despite the time and effort spent growing these emeralds, they still don’t compare in value to naturally grown emeralds.