It is performed by passing chemicals (solvents) over raw dried bud. The chemicals dissolve the cannabinoids and hold them in solution after the plant matter is removed. The chemical is forced to evaporate leaving behind a liquid or solid that is all but pure cannabinoids. The process is done cold which preserves the THC and THCa but also means the THC and THCa require decarboxylation (applying heat) which makes this extract unusable for edibles. There are several different types of solvents used that fall into the general category of hydrocarbon extraction but the main one used for Shatter is n-Butane (C4H10o).
Extraction procedure begins by packing raw buds or any plant material that contains THC into a tube or pipe and then forcing butane through the plant material from one end to the other. The butane drips out and is collected in a tray. The shiny pale yellow semi-liquid is then allowed to evaporate and the resulting concentrate is an oily substance aptly called butane hash oil (BHO). Many factors determine whether the final product will be a brittle Shatter(preferred) or a Snap and Pull taffy Shatter. We won’t go into those now.
The best part of extracting THC is that you can utilize almost 100% of the plant since you are just striping the THC off and not smoking the plant. Trimmings, stock and shake can all be ground up and washed with Butane, leaving behind only the THC.
Read more about butane extraction.