Most common cartridges that are sold in dispensaries are primarily composed of cannabis distillate. A cannabis distillate is a concentrate that has been further refined through a process called fractional distillation to separate the remaining constituents by molecular weight. This distillate is usually a thick honey consistency and is made slightly less viscus by reintroducing terpenes or a cutting agent like propylene glycol or vegetable glycerin for use in pens. Needless to say its not a simple process. Although, in light of the inflated cost that dispensaries charge for most cartridges (the standard 1/2 gram of this stuff cost at most $3 to make and the cartridge itself avg about $1.50) I can give you a slightly simpler, less hardware intensive alternative.
Take a jar with a screw on lid and add some of your favorite organically grown green goodies pour in some very cold grain alcohol (ever clear will do the trick) until your goods are submerged and screw the lid on nice and tight. Shake well,( hint..the better your goodies are broken up the better the alcohol will be able to strip off the cannabinoids) after a minute or two of shaking remove the lid and pour the contents through a strainer to separate the liquid from the plant material. You will then take the remaining liquid and stick it in the freezer for at least 24 hours ( this step could take longer depending on the temp of your freezer. After at least 24 hours take out your jar of goods out and strain again. This time you will notice little fatty/waxy clumps floating around, these are the lipids from the plant and this process of removing them is called winterization. After straining, if you would like to insure a thorough winterization do this process again. Subsequent to this there are additional steps to "lighten up" your product such as mixing in activated carbon to a warmed solution or performing water washes with various solvents but for simplicity sake we can stop here and allow our alcohol to evaporate off leaving behind a concentrate rich in cannabinoids. Please note some individuals choose to use heat to expedite the evaporation process using heat. if this is your intension remember alcohol and its steam are extremely flammable DO NOT USE AN OPEN FLAME WHILE EVAPORATING.
Once the alcohol has evaporated and you’re left with a thick very sticky solution it can helpful to use heat to ensure that all that your concentrate is alcohol free. Place a culinary thermometer in to the concentrate and gently warm it with an induction cooker or another flame free heating option, alcohol"s boiling point is 173 Fahrenheit so you want to make sure you exceed this to ensure all alcohol has been vacated. Decarboxylation, the process of removing the acid compound to make theca bio-available starts at around 220 Fahrenheit, and THC itself oils off at 315 Fahrenheit. If you plan on smoking the concentrate than it will be decarbed for you in the process, if not go ahead and decarb it so it will be activated for ingestion or topical use if you desire to experience the psychoactive effects.
Hope this helps