The essence of a thing is the basic or true nature of the thing. It also refers to a fragrance. Or the concentrated form of something, especially a plant, obtained through distillation.
Among magical people, the word essence appears in a lot of different contexts.
Spagyric elixirs are also often referred to as essences. These combine a tincture of a plant with a distillate and the salts extracted from the ash of the same plant. Through spagyric methods, all of the fat and water-soluble components are mixed with the minerals in the plant to create a perfect remedy that captures the pure essence of the herb without the extraneous material.
A lot of today’s older cooks refer to what is now marketed as extracts as essences. (Like vanilla extract, orange extract, almond extract, mint, etc.) These are basically tinctures and generally made using about a pint of good, strong alcohol per two ounces of vanilla beans, orange/lemon, etc. peels (just the zest, the colored part, not the white part), dried leaves, etc. cover, and let rest in the dark for a season, then strain and store in a cool dark place. These are used for flavoring food, as well as for fragrance purposes, and they can end up in a floor wash or mundane cleaning solutions as well.
The extraction of essential oil through distillation probably what springs to mind today. This preserves and concentrates the herb’s fragrance and other fat-soluble constituents. But essential oils are very concentrated and thus often much too strong to be used directly. It is also costly as it often takes several pounds of plant matter to create a very small amount of oil. Thus, the essential oil is often diluted, but since oil and water do not mix, a neutral oil or alcohol is preferred. Back in the old days, when I was young, the old ladies referred to a mixture of a single oil in alcohol as an essence; essence of rose, essence of orange, essence of lavender, etc. Sometimes they called it “water” rather than essence, which, I believe is more common. It was basically a simple toilet water, but they were primarily used to scent sheets and things or added to a floor wash. An ounce of oil to a pint of alcohol is a good ratio. And, because they were grannies, it didn’t have to be pure essential oil. Candy flavoring oils and perfume oils, synthetic or otherwise got used just as often.
Nowadays, the term essences often refers to Bach’s flower remedies. These were first presented by Dr. Edward Bach in the 1930s and have become quite popular homeopathic remedies. These essences are energetic, rather than physical as the remedies are said to contain the energetic signature of the plants and, indeed, tend to contain very little actual plant material. A mother tincture is made (actually an infusion or a decoction) and it is further diluted in water or alcohol before administering it to the patient. Thus, homeopathic remedies might contain the signature of a toxic plant, but no actual toxins or such tiny amounts as to be negligible. These are said to work primarily on the emotions, as Dr. Bach believed that all disease stemmed from emotional disturbance. Visit The Bach Center’s Website to learn more. You can download a PDF version of his 1930s book Heal Thyself there too. It is interesting to note that the remedies are nowhere on the site or in the book called “essences”, and, I personally would have been inclined to call them elixirs, so I’m not sure where the vernacular came from.
I have also heard the term crystal essence used synonymous with the term crystal elixir. Which is more correct, I can’t say.