Fun article about perfume (and an Italian perfumer)

 Sitting here on vacation, I came across this fun New York Times Magazine article about a perfumer in Parma, Italy: 

...The final bottle of perfume went around the table. This one, called Avatar, mimicked the experience of entering a gelateria. It was the most unnervingly evocative of the three lunch scents. At first spritz, it smelled like cold marble, polished glass, wiped surfaces. Ten minutes later, the scent was that of gelato: cream, egg yolks, white sugar. Later that evening, long after lunch was over, I sniffed my left wrist and nearly shrieked. The cold marble and sugared cream had vanished. In their place was a smell that didn’t exist earlier, that seemed to arise from nothing. It was the smell of freshly baked ice cream cones. What sorcery was this?

Not any kind of sorcery, actually, if you are a chemist. Smells are made of molecules, which come in different sizes and weights and levels of complexity. Some odor molecules are detectable by humans, but in order for us to smell one, it must evaporate from wherever it lives — a ripe nectarine, a gym bag — and physically enter the nose. Because the smelly molecules that make up a perfume come in various shapes and weights, they escape and fly into noses at different rates. Some zoom up there instantly; others stubbornly refuse to take wing until hours have passed.

When perfumers — or the promotional materials that accompany a perfume — refer to top notes, middle notes (or heart notes) and base notes, this is what they mean. The molecules that evaporate speediest are the first to reach your nose, as well as the first to disappear entirely. Top notes are ephemeral. If you buy a fragrance based on the top notes, you’ll be forever trying to write a check that chemistry can’t cash. After the coy top notes come the sturdier middle notes, which have a slower rate of evaporation. The base notes last longest, sometimes through several showers. If you know the rate at which each layer evaporates, you can program a fragrance like a piece of software...

I'm sure this is well-known to perfume chemists, but I wasn't aware. Cool article.