The top notes(highnotes) are the most volatile ones in the blend – the ones you’ll smell first, and also the ones that will evaporate first as you wear your blend. They form the first impression your perfume makes, and should “lead” your nose into the heart of the perfume by harmonizing well with the other notes.
The heart notes (also called middle notes or coeur notes) are the … well, the heart of a fragrance/perfume! They aren’t as volatile as the top notes, so they emerge a bit later and last longer. They should give your scent roundness and fullness and complexity.
The base notes have two functions in a perfume. First, they’re the least volatile elements, so they emerge more slowly, and their aroma will remain the longest. So it’s very important to make sure you like your base note! Second, they can have a “fixative” effect on the entire blend, keeping the top and middle notes from evaporating as quickly.
Natural essential oils and absolutes are complex, so very few of them are only top notes or strictly middle notes or
inarguably base notes. Most of them have top-note and middle-note components, or middle-note and base-note
components. Some of them include notes from the whole spectrum.
Also, because they’re natural products, they can differ widely from batch to batch – your geranium eo, for example, may have much more of a top-note character than mine. So the categorizations below are only guidelines; you have to work with your own eo’s to learn how they behave. Also, I’ve only mentioned oils that are relatively easy to find; there are many many more that are fascinating and wonderful additions to perfume blends, if you decide to search off the beaten track.
Top Notes(High notes): citrus oils (bergamot, lemon, mandarin, orange, etc), conifer oils (cypress, fir, pine, spruce, etc), mint oils, basil, cardamom, chamomile, ginger, juniperberry, petitgrain, rosemary
Middle Notes: floral oils/absolutes, black pepper, caraway, cinnamon, clary sage, clove bud, coriander, elemi, galbanum, geranium, lavender, sweet marjoram, nutmeg, palmarosa, thyme, violet leaf absolute, ylang ylang
Base Notes(low notes): wood oils (cedarwood, gaiac, linaloe wood, sandalwood, etc.), resin oils (frankincense, myrrh, etc), labdanum, oakmoss absolute, patchouli, vanilla, vetiver
In the early days of perfumery, oils made from animal products were also frequently-used base notes: ambergris, civet, musk, etc.