Centrales nucleares

Botanical source

The botanical identity of the source plant is basic information for defining a bioactive essential oil, along with the specific part of the plant used to distill the oil. Both are important because different species usually yield oils of a different quality and character; e.g. the Helichrysum species distilled in Madagascar are very different from the one species produced in the Mediterranean. Likewise, a single plant can yield different oils from different parts; e.g. Juniper berry and Juniper twig oil, Cinnamon bark oil and Cinnamon leaf oil; Pimenta berry and Pimenta leaf oil.

Other names

Alternative English names in common use for the oil or the plant are given, along with its names in other major languages.

Appearance

This describes the mobility, colour and odour of the essential oil, which together are its key identifiers from the organoleptic point of view. Any significant differences in appearance and aroma usually point to an element of adulteration. Minor differences may also simply indicate a deterioration of oil quality, which is usually due to oxidation or polymerization from poor storage and/or ageing.

Mobility

Most essential oils are approximately as mobile as water; others range from somewhat thicker (Palmarosa, Peppermint, Ylang ylang) to quite syrupy (Cistus, Patchouli,

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Sandalwood) to highly viscous (Vetiver, Myrrh). Most of the viscous oils are high in sesquiterpenols, e.g. patchoulol in Patchouli, vetiverol in Vetiver and santalols in Sandalwood.

An important clinical consequence of high viscosity is that it increases the drop size of the oil dramatically, which is a consideration in formulating work of any kind. Absolute extracts are generally also fairly thick, as with the absolutes of Rose, Jasmine, Tuberose, Champaca, Patchouli and so on. Some, like Balsam fir and Clary sage absolute, are solid at room temperature.

Colour

While the whole colour spectrum can be seen in the oils in common use, the two most common shades seen are clear, like water (as seen in Eucalyptus and most conifer oils), and pale green-yellow (e.g. Tea tree, Clary sage, Palmarosa, Frankincense). Others are various shades of green (Bergamot, Clary sage), deep amber (Vetiver) and olive brown (Patchouli, Spikenard, Vetiver). The cobalt blues of German camomile, Blue tansy, Yarrow and Blue cypress, from their chamazulene content, is very striking.

It is tempting to make systematic associations between an oil colour and its basic quality and typical clinical functions. One can draw from several models to create these associations, e.g. the Western four elements, the Oriental five-element system, the yogic seven chakras, all of which have strong traditional colour associations. While this approach is perfectly valid, we should remember that not all oils express themselves in colour. There is an inherent limitation then to obtaining therapeutic information from the colour of an essential oil alone.

Odour

This is the most important identifier for an essential oil, as much adulteration (but not all) can be detected experientially through its aroma. Essential oil odour is largely the result of oxygenated compounds in combination, especially alcohols such as monoterpenols and sesquiterpenols; but also esters, aldehydes, ethers, ketones and acids. The weakest aspect of describing oil odour is simply language itself, which is frankly poorly developed in defining the many small nuances found in the odours of natural plant materials. This reflects the relatively minor role of scent in Western culture, science included, especially in comparison to sight (Ackerman 1990). Still, there exists a small but solid body of terms used by perfumers that almost everyone seems to share and understand. Arctander’s reference work on perfumery materials (1960) is a current example of the most useful categorization and description of the spectrum of essential oil odours.

Perfumery status

Essential oils are important components of high-class and ‘natural’ perfumery. Moreover, although perfumery and the creation of aesthetic blends is clearly not the focus of this text, it is still important that the therapeutic blends be considered pleasant, especially if they are being diffused in the environment for any length of time. For this, knowledge of fragrance aesthetics can be very helpful.

To create a treatment blend that is not just effective, but also highly acceptable, we need to understand the fragrance aesthetics of essential oils both singly and blended. This will ensure not just user-friendliness, but also client compliance. Clients will reject an unpleasant blend, regardless of any positive suggestions given by the therapist. The placebo effect can easily be made almost non-existent. Olfaction in a therapeutic context is here clearly in marked contrast to ingestion, where having to drink decoctions of awful-tasting medicinal herbs (as in some Chinese herbal decoctions) is often the norm and largely manageable. The ‘pleasant’ versus ‘unpleasant’ factor of olfaction ultimately depends on the limbic system. Unlike with all other sensory input of information, the limbic system does not rely on the thalamus to reduce and attenuate the olfactory information it receives from the external environment. The limbic system simply desires pleasant aromas for individual survival and will not tolerate anything else. While it prefers complex over simple fragrance notes, it will still tolerate simple aromatic combinations as long as it deems them pleasant and they do not create olfactory fatigue.

What, then, constitutes a pleasant aromatic blend? First and foremost, one that takes the aesthetic laws of fragrance into consideration. Such a blend will be considered pleasant, i.e. non-fatiguing on prolonged exposure and positive in connection with repeat usage. This is emphatically not to say that treatment blends for inhalation with diffusers, nebulizers, etc., should conform to the classic formula of perfumery, where head, heart and base note oils must all be present is general proportions. Our aim here in a clinical context is to create a therapeutic blend, not a perfume. On the contrary, because treatment blends are deliberately one-sided in one way or another, they tend not to include all three scent notes. They will usually be top heavy, bottom heavy or middle heavy, and sometimes heavy in the two adjacent categories. It is possible, for instance, to make a therapeutic blend of mainly head notes with a minor amount of heart notes to increase acceptability and therefore client compliance; or mainly base notes with small amounts of heart notes to keep the whole blend alive.

The main three aesthetic aspects of fragrance are its note, intensity and persistence. In a treatment context, only the first two aspects are ever a real consideration in the creation of a blend or formula.

The fragrance note

Fragrance notes largely result from their degree of volatility, i.e. the rate at which they evaporate. They come in three categories: head, heart and base notes, and can

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be understood as the relative ‘pitch’ of essential oils. Creating a satisfying proportion among the three notes is a major consideration in the creation of an aesthetic or perfume blend, while in therapeutic formulation it is a secondary issue.

• A head note oil is often described as ‘fresh’ and is usually pungent or lemony in fragrance. It has a high degree of volatility and a light, sharp, penetrating character that gives a blend lift, movement, clarity and, ultimately, lyric interest. Head notes are perceived first in a well-balanced fragrance composition; they are its introduction. Lemon, Grapefruit, Bergamot, Lime, Mandarin, Grand fir, Lemongrass, May chang, Lavender, Eucalyptus, Peppermint, Spearmint, Cajeput, Saro, Niaouli, Cardamom, Nutmeg and Black pepper are all typical head note oils.

• A heart note oil is usually floral, sweet, green, ambery or spicy. It is moderately volatile; it has a balancing, harmonizing, unifying character that gives a blend body, warmth, fullness and coherence. Heart notes are perceived after head notes in a well-balanced composition and literally form its heart or central core. They express the main aesthetic statement of a blend. In that sense they are the most important of all three notes. Good heart note oils include Geranium, Rose, Palmarosa, Helichrysum, Neroli, Jasmine absolute, Jasmine sambac absolute, Ylang ylang, Blue tansy, Clary sage, Roman camomile, Marjoram, Galbanum, Clove, Ginger and Cinnamon.

• A base note oil is usually woody, rooty or mossy. It is poorly volatile and has a dark, heavy, static character that grants a blend depth, glow, richness and presence. In a well-balanced composition, base notes are perceived last of all after heart notes and play a supportive role to them. Their presence will make a blend complete. Vetiver, Cedarwood (all types), Patchouli, Cistus, Sandalwood (all types), Spikenard and Frankincense are common base-note oils. Many absolute and other tpes of extracts possess a good base note, including Cistus, Oakmoss, Patchouli, Benzoin, Peru balsam, Lavender, Clary sage, Cacao, Coffee and Balsam fir.

The fragrance intensity

Fragrance intensity refers to an oil’s relative loudness or softness and is divided into high, moderate and mild. This is a major consideration in the creation of an aesthetic or perfume blend, while in therapeutic blending it is again of secondary importance.

• A high intensity oil has a strong aroma and may be either intensely sweet- floral or strongly fresh-pungent. Oils that exhibit a high intensity include Blue tansy, German camomile, Yarrow, Helichrysum, Ylang ylang extra and no. 1, Petitgrain, Cinnamon, Basil (most types), Cardamom, Marjoram, Eucalyptus, Ravintsara, Cajeput and Niaouli. Smaller amounts of these are often used in blending work.

• A moderate intensity oil is moderately strong and represents the majority of oils used.

• A mild intensity oil has a weak aroma and includes many woody oils, such as Myrrh, Atlas cedarwood, Patchouli and Sandalwood, as well as more subdued green oils such as Lavender, Clary sage and Hyssop.

The fragrance persistence

Also called tenacity, this refers to the duration or length of time that an oil will stay on the skin. This is only a consideration when the aim is to create a perfume rather than a therapeutic blend.

• Excellent persistence means the oil has excellent staying power on the skin; e.g. Vetiver, Helichrysum, Patchouli, Cistus, Atlas cedarwood, Sandalwood, Spikenard, Ambrette seed. Many, but not all, are base notes.

• Moderate persistence indicates the oil as having moderate staying power on the skin; e.g. Geranium, Palmarosa, Clary sage, Rose, Fennel. The majority are heart notes.

• Poor persistence means the oil has poor staying power on the skin because of rapid evaporation, e.g. Bergamot, Lavender, Eucalyptus, Sweet orange, Pepper-mint, May chang, Lemongrass and Grapefruit. Most of these are head notes.