Entering perfumista territory some years ago, I learned that two criteria capture a perfume's performance: longevity/tenacity and sillage. Clearly, time and distance are the two dimensions we are interested in, when evaluating performance.
Calkin and Jellinek (1994) define the following performance criteria, which have become standard in the fragrance industry:
Impact is an immediate olfactory sensation and is a measure of the intensity of a perfume in the first moments after application, e.g., when sniffing a perfume from a blotter or right after its application onto the skin.
Diffusion refers to the efficacy of a perfume at some distance from the source, representing how fast a fragrance radiates in space and permeates into the surrounding environment.
Volume is the effectiveness of a perfume over distance, sometime after application.
Tenacity is the ability of a fragranced mixture to retain its characteristic odour during the dry down stage. It is a performance index that measures the persistence of a fragrance for long times after its application but near the evaporating source, e.g., how long the perfume lasts on skin after applying it.
Lit.:
Calkin and Jellinek (1994), Perfumery, Practice and Principles
Teixeira et al. (2013), Perfume Engineering, Design, Performance & Classification
Sillage – an undifferentiated layman term?
Quite some fragrances feature excellent diffusion and tenacity but are moderate or even low in volume. Sillage, however, does not capture this time-dependent aspect of a perfume's presence over distance and therefore I increasingly view it as an insufficient term.
My, albeit limited, discussions of this topic with perfumers revealed that sillage, in the context of perfumery, is an unknown term which seems to be primarily used by perfume bloggers and on perfume fora. Who would have thought?
Yet, it obviously exists in perfume lingua. For example, Oxford Dictionaries define sillage as "[t]he degree to which a perfume’s fragrance lingers in the air when worn".
What are your thoughts on its usefulness as opposed to diffusion and volume?