The world of perfume is so insular, it seems I can never find the answer I am looking for. I was reading an article with Luca Turin opinions in it, and he mentioned how for cheap perfumes all of the notes are on the top to make the customer buy faster, and that's why they last so little, so I started thinking, how do they layer the notes in a perfume? How do they make it so that all the scents aren't gone or smelled simultaneously? I know some notes are heavier than others and that's how they last longer but how does this chemistry actually work??