Bài 6 · Những chất giữ mùi ở lại

Five blotters side by side, the same orange accord, four of them with one slow material added: benzoin, vetiver, myrrh, vanilla. Lesson six of the blending course measures how much longer a fixative holds the light part, and what scent it brings with it.

Two blotters side by side

The experiment starts with two blotters. The first is dipped in a diluted sweet orange solution. The second is dipped in the same solution with a small share of fixative added. Both are timed and set side by side. There is only one question: on which blotter does the orange remain recognisable longer.

Sweet orange is chosen because it is one of the fastest oils to leave a blotter. Limonene makes up 86 to 96 percent, and the library's volatility chart estimates sweet orange at about 6 hours on a blotter. An orange accord is where the effect of a fixative, if there is one, shows most easily.

In lesson five, the added materials worked in the opening and the heart, turning the accord. Lesson six goes down to the lowest tier. The added material this time is not meant to change direction but to change time.

The experiment extends to five blotters: one control with orange only, four with four different plant fixatives. Each holds eight parts orange accord to two parts fixative, all diluted to 10 percent in alcohol. The ratio stays the same across blotters so that the only difference is the fixative.

What slow evaporation means

Every molecule leaves a blotter at its own speed, set by its vapour pressure. High vapour pressure molecules reach the nose first and fade early; low vapour pressure molecules linger. Most fixatives are large, heavy molecules with very low vapour pressure.

The library's glossary defines a fixative as a low volatility material used to slow the evaporation of lighter parts and extend a scent. The definition comes with a cautious clause: how much it actually slows evaporation varies case by case. A fixative does not lock a scent. It slows it, and the slowing has to be measured.

The simplest measure is to note when the orange stops being recognisable on each blotter. The smelling rhythm is tighter than in earlier lessons: fifteen minutes, thirty minutes, one hour, two, four, eight, then one day. With orange, the first hours are where everything happens.

Room temperature and air movement affect the result more than expected. The five blotters should stand in the same place, away from fans and sun, and each smelling should keep the same distance from blotter to nose. The library's volatility chart also notes that temperature, dilution and lot all shift the figures.

The result of this lesson is a span of time, not an impression. At what hour the control loses its orange, at what hour the benzoin blotter does. The gap between the two figures is the added tenacity the fixative gives, on a blotter, with that particular lot of orange and that particular fixative.

Benzoin resin and vanillin

Benzoin is the dried resin of Styrax trees. The library records two commercial streams: Sumatra benzoin and Siam benzoin, the latter largely from the Luang Prabang region of Laos. Benzoin has no distilled essential oil in the usual sense. The commercial material is a resinoid or absolute, a sticky mass, usually diluted to 50 percent in benzyl alcohol, benzyl benzoate or DPG to be workable.

The volatile part of benzoin is mainly benzyl benzoate, 39 to 51 percent, and benzyl alcohol, 39 to 43 percent, with benzoic acid and some cinnamates. Benzyl benzoate is itself used as a fixative in perfumery. Benzoin is heavier than water, and the library notes that it does not dissolve in fixed oils, a detail lesson seven returns to.

Vanilla takes another route. The pods are picked green, then processed over 6 to 9 months of sweating and slow drying. During that time vanillin is released from its glycoside form by enzymes. On the volatility chart vanilla lasts 400 hours or more, measured at 20 percent. The library notes that over 95 percent of commercial vanilla flavour is synthetic vanillin.

Benzoin and vanilla sit side by side in the library's substitution chart: both give a warm balsamic sweetness. The library also lists vanillin among the materials that may be added to benzoin to strengthen its scent. On an orange blotter, these two tend to pull the end towards sweet and round.

Vetiver: root and earth

Vetiver is a grass with roots that reach 3 or 4 metres deep. The roots are harvested after 18 to 24 months, dried, then distilled for 24 to 48 hours. The long distillation is needed to draw all the heavy compounds out of the root. Haiti is the largest producer; in Vietnam vetiver is grown mainly to hold soil against erosion.

Vetiver's composition is a characteristic group of sesquiterpenes: khusimol at 3.4 to 13.7 percent, the vetivones, vetivenenes, vetispirene. No single one dominates. The library describes its scent as earthy, woody, smoky, balsamic, with a note of rum, and states that it is a lasting fixative.

On the orange blotter, vetiver works differently from benzoin. Benzoin pulls the end towards sweetness; vetiver pulls it towards dryness and earth. At two parts in ten, vetiver may already be obvious from the start, because its odour strength is high. The library's pyramid tool groups vetiver with cinnamon and clove as oils that need only a small share.

Vetiver, like patchouli, is one of the few oils valued with age. The library notes that vetiver aged 5 to 10 years is smoother and more complex than fresh oil. An old lot and a new lot of vetiver can give two different results on the same orange blotter.

Myrrh and dry resin

Myrrh is the resin of Commiphora myrrha from the semi arid regions of Somalia, Ethiopia and Yemen. When the bark is damaged, a pale yellow sap flows out and hardens in air into reddish brown lumps. The dried resin is cleaned, then steam distilled, with a yield of about 3 to 8 percent.

The oil is made of furan compounds rarely found elsewhere: furanoeudesma-1,3-diene at about 34 percent, furanodiene at about 20 percent, lindestrene at about 12 percent. The library describes the scent as resinous, warm, slightly bitter, balsamic, woody. On the volatility chart myrrh lasts 400 hours or more.

On the orange blotter, myrrh brings a bitterness and dryness to the end that benzoin lacks. It belongs to the Burseraceae family, like frankincense. Beside it among the resins is labdanum, a resin from the leaves of cistus in Spain, warm, balsamic and ambery, a classic base material of the Chypre family.

Myrrh is the material in this lesson that most needs a safety note. The library lists it as strictly contraindicated in pregnancy and breastfeeding, by all routes, because of its β-elemene and furanodiene content. The oil also thickens under poor storage; the library's storage page lists myrrh among oils prone to resinification, so it should be kept dark, sealed and cool.

A fixative is also a scent

By the eighth hour, the control blotter usually holds only a faint trace of orange, or nothing. The fixative blotters still smell. The harder question is what they smell of. It may be orange that has stayed longer. It may also be that the orange has gone and what remains is only benzoin, vetiver or myrrh.

To tell the difference, four more blotters are needed: each fixative on its own, at the same dilution. Smelling the orange and benzoin blotter beside the benzoin alone blotter, the difference is the orange that remains. Without this control it is easy to mistake the fixative's own scent for the tenacity of the accord.

A fixative must therefore be counted in the accord from the start, as a material with its own scent, not an invisible additive. Two parts benzoin in ten are two parts balsamic sweetness. Two parts vetiver are two parts dry earth. The orange accord with a fixative is a new accord, and it needs a new series in the manner of lesson four.

After this lesson the scent notebook holds two time columns for each fixative: the hour the orange disappears on its own, and the hour it disappears with the fixative. Lesson seven takes the accord from blotter to bottle: alcohol or carrier oil, the concentration, and time to do the rest.

A fixative does not hold a scent. It only makes the leaving slower.

What remains on the blotter at the end of the day is not always what was dipped at the start.

Time has a scent too.