An apple pie baking in the oven smells both strong and pleasant. Skunks release strong and offensive odors. A glass of water smells neither strong nor offensive because it has no smell at all. Odor Persistence Perfumers are masters in the art of blending many odors to form complex mixtures known as perfume. If one distinct odor is a note, then a mixture of many odors is a chord.
Perfumers also recognize that a chord of odors can change with time.
Perfumers group notes according to their relative volatility or persistence. The most persistent odors are base notes. The least persistent odors are top notes. Odorants with medium volatility are called middle notes or modifiers. When perfume is placed on the skin, the first scent smelled is the top note.