Scent Trails

Sillage may only be a two-syllable word, but it’s a fluctuating component of scent that encompasses a multi-faceted network of physics, chemistry, and aesthetics. Geza Schoen explains the factors which cause some scents to whisper and others to shout.

Marcel Proust famously wrote: “When nothing else subsists from the past, after the people are dead, after the things are broken and scattered…the smell and taste of things remain poised a long time, like souls… bearing resiliently, on tiny and almost impalpable drops of their essence, the immense edifice of memory.” Since Proust’s heyday, we have come to know this phenomenon as sillage, or the French word for “wake”. But what is the science behind the invisible trail of scent a fragrance leaves behind?

It turns out the answer, much like perfume itself, is complex. “There’s not an exact formula for it,” explains Geza Schoen. “Part of it is vapour pressure, which tells you how fast a molecule will evaporate. Another is strength of ingredients; especially powder materials, such as sweet and musky notes, have excellent sillage as they stay in the air longer. But when putting a fragrance together, it’s complicated because you combine so many different ingredients with different vapour pressures, different capacities, different lasting power, and different overall power.”

These fluctuations occur in both naturals and synthetics. “It differs enormously. Something like patchouli, for example, has longevity, is strong, and gives you big sillage, especially if you combine it with other ingredients which have similar traits. But not all naturals, or all synthetics, last very long, and naturals could also suppress the blooming of a sillage because of their complexity,” he states. Generally speaking, hesperidic (i.e. citrus) and green notes have a reputation for being especially fleeting, whereas oud and vanilla have an impressive projection power.

In traditional fragrance structures containing a top, heart, and base note, those ingredients with a higher vapour pressure (those which are more fleeting), and often more lightweight character and concentration, sit at the top of the pyramid. As the fragrance unfolds, it gives way to an increasingly deep and dense construction of notes, ending in the inevitable dry-down which lingers on the skin.

However, so-called linear fragrances, which maintain the same olfactory character throughout, as well as structural manipulation, can put a twist on these usual operations. “It is possible to have the base note boosting straight through to the top note because some of them are so heavy that you would instantly smell them. Prolonging the smell of the top note into the dry-down is more difficult, simply because of the high vapour pressure,” Schoen states.

Longevity is a consistent, but not guaranteed, partner of sillage. Whereas the former denotes the length of time a fragrance wears on the skin, sillage determines the volume. “Each ingredient is different,” Schoen adds. “For example, Molecule 01’s Iso E Super is not a strong smell at all. 90 percent of all other perfume ingredients are way stronger, yet it has incredible longevity and a very subtle and silent, but extraordinary, sillage.”

The formula of a fragrance, or strength of dilution (the percentage of aromatic compounds in an alcohol base), also comes into play — alongside the puzzle of ingredients that constitute a scent. “A cologne fragrance, something fresh, green, light, and fruity, but not heavy, sweet, or woody would probably evaporate quicker,” Schoen states. “But if you want to create a long-lasting eau de toilette, with a concentration of 8-12%, you just need to put in a lot of materials which, even at a low dosage, are long-lasting. If you have an eau de parfum dosage, you can go up to 20-25%, which allows you to work more subtly with the fragrance ingredients that aren’t that strong.”

When one sprays a fragrance on the skin, the alcohol is the first thing to evaporate, hence why perfumes with a higher concentration last longer: there is less material to float away. However, the alcohol can also give a scent its airborne wings, a beautiful transparency that allows it to waft about rather than cling to the skin. For example, in most instances, alcohol-free perfume oils will wear closer to the skin than their atomised counterparts.

Speaking of skin, or its chemistry specifically, the body wearing the scent can have just as much of an impact on how loudly a scent can project on us. Think skin type, gender, lifestyle factors such as diet and exercise, even geographical location which determines the level of perspiration and therefore fragrance evaporation.

Physics, chemistry, dilution, formulation, climate, physiology — sillage may be a single term, but it encompasses a vast variety of components and variables. Technicalities aside, it ultimately raises a debate on cultural as well as personal aesthetics.

In the 1980s, bars and restaurants famously banned patrons who wore Giorgio Beverly Hills, and food/travel writer Jason Kessler implored audiences (and potentially governments) to ban garishly loud fragrances in restaurants nationwide. “Ideally, when you are creating a fragrance, you want other people to smell it. Otherwise you might as well not wear one. You can turn it into a scent bomb if that goes along with the parameters of your conceptual approach, but I don’t like them,” Schoen remarks. “I find it invading. Why expose someone with something they might not want to smell?”

In some cultures, heavier scents are a component of everyday life, whereas in others it is considered impolite to wear bold fragrances in public spaces. Certain scenthusiasts will decry a fragrance for not having potent longevity and projection and therefore being a failed investment, while others enjoy the allure of a scent which beckons those around us to lean in a little closer. Sillage may not be simple, but it’s an integral part of making the personal decision of whether you want to be olfactorily daring or discrete.

Read the full article here.

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