The second way to classify oils is by Evaporation Rate.

This method sorts essential oils using the analogy of a musical scale. Septimus Piesse was a 19th Century English perfumer who speculated that there were similarities in the ways humans experience both sounds and smells. A major chord, for instance, consists of a root note, a major third interval, and a perfect fifth interval. When these precise pitches come together in harmony, our brain registers a pleasing and balanced sound. Maybe the scents of essential oils work in the same way?

Essential Oil Diffuser

It was eventually uncovered that there was some validity to the theory Septimus Piesse suggested. Today, the perfume and essential oil industry commonly places essential oils into three overarching 'notes', each of which portray a distinctive quality and rate of evaporation.

Essential Oils in the ‘high’ note have a low molecular weight, and therefore hit the olfactory receptors first when you inhale an aromatic blend. It also evaporates very quickly, which causes the blend's aroma to evolve and make the other notes much more prominent.

The rate of evaporation of the middle note is not as quick as the high note, but it is still faster than the base note. This middle note acts as an essential 'bridge' between the lighter and heavier oils within a blend, bringing in a sense of harmony, symphony, richness, and balance.

The base note relates to the essential oil that has the highest molecular weight. They take much longer to evaporate. It also 'retains' or 'fixes' the rest of the elements of the blend, making the fragrance more secure, binding, and longer-lasting.

 

PERFUME NOTE

EVAPORATION RATE

COMMONLY USED ESSENTIAL OILS

Top

0.5 - 3 hours

Bay, Citrus Oils, Eucalyptus, Lavender, Mint Oils, Petitgrain, Pine, Rosemary, Sage

Middle

2 - 4 hours

Black Pepper, Clove Bud, Cinnamon, Fir Needle, Geranium, Marjoram, Myrrh, Palmarosa, Rose Absolute

Base

Up to several days

Cedarwood, Frankincense, Valerian, Vetiver, Spikenard, Patchouli, Sandalwood

 

Using the ‘perfume note’ theory, we can create fragrances or blends that exhibit preferred characteristics. For instance, choosing an oil from all three perfume notes (top, middle, and base) can help create a more complex, well-developed blend that enhances and unfurls over time. In contrast, choosing oils within the same perfume note can give rise to a more homogeneous blend that is uniform in its smell and performance.