Extraction is a process by which butane gas is used as a solvent to extract chemicals from herbal matter.
The technical name for extraction is actually supercritical fluid extraction. This is a process in which commercially available butane gas is used as a solvent. The only other materials needed are a length of PVC pipe (it does not have to be the threaded variety) and two end caps.
The reason why this process is so effective is that butane (and possibly a number of other untested solvents with extremely low boiling points) can extract only the most essential components from herbal matter, producing an oil of the highest quality and leaving the undesirable remnants behind. In fact, this process is so efficient that it can produce a remarkably high-quality oil from even the lowest quality herbs.
One of the main drawbacks of this process is that it produces a very small amount of oil. This is definitely not the ideal method to use if your herbs are in short supply and you want to get the most out of your plant matter. In general, you can expect to derive about a gram of oil from an ounce of standard herbal matter, and up to a maximum of 3 grams from an ounce of high-quality herbs.
While the low volume of oil produced by the extraction process may be a bit of a drawback, you have to consider that the potency of oil produced is extremely high. The oil that you can obtain from extraction is undoubtedly more potent than any herbs you can buy.
Potency aside, the composition of the oil also makes the process worthy of consideration. The oil produced from extraction is about as pure as you can get outside of carefully controlled laboratory conditions. If the process is done right, what you will get is a remarkably high-quality oil with a rich amber color.
Since virtually all of the impurities in herbal matter are left behind during the extraction process, the resulting oil is significantly less harmful to health. This makes extracted oil a much better choice for those who consume herbs for medicinal purposes.