Perfume

===Technique===
[[File:Blotter strips.jpg|right|thumb|Paper blotters (fr:''mouillettes'') are commonly used by perfumers to sample and smell perfumes and odorants.]]
Although there is no single "correct" technique for the formulation of a perfume, there are general guidelines as to how a perfume can be constructed from a concept. Although many ingredients do not contribute to the smell of a perfume, many perfumes include colorants and [[antioxidant]]s to improve the marketability and shelf life of the perfume, respectively.

====Basic framework====
Perfume oils usually contain tens to hundreds of ingredients and these are typically organized in a perfume for the specific role they will play. These ingredients can be roughly grouped into four groups:
*''Primary scents'' (Heart): Can consist of one or a few main ingredients for a certain concept, such as "rose". Alternatively, multiple ingredients can be used together to create an "abstract" primary scent that does not bear a resemblance to a natural ingredient. For instance, jasmine and rose scents are commonly blends for abstract floral fragrances. [[Cola]] flavourant is a good example of an abstract primary scent.
*''Modifiers'': These ingredients alter the primary scent to give the perfume a certain desired character: for instance, fruit [[ester]]s may be included in a floral primary to create a fruity floral; [[calone]] and citrus scents can be added to create a "fresher" floral. The cherry scent in cherry cola can be considered a modifier.
*''Blenders'': A large group of ingredients that smooth out the transitions of a perfume between different "layers" or bases. These themselves can be used as a major component of the primary scent. Common blending ingredients include [[linalool]] and hydroxycitronellal.
*''Fixatives'': Used to support the primary scent by bolstering it. Many resins, wood scents, and amber bases are used as fixatives.

The top, middle, and base notes of a fragrance may have separate primary scents and supporting ingredients. The perfume's [[fragrance oil]]s are then blended with [[Ethanol|ethyl alcohol]] and water, aged in tanks for several weeks and filtered through processing equipment to, respectively, allow the perfume ingredients in the mixture to stabilize and to remove any sediment and particles before the solution can be filled into the perfume bottles.<ref name=cbyear>{{Cite book| first=Chandler| last=Burr| title=The Perfect Scent: A Year Inside the Perfume Industry in Paris & New York| publisher=Henry Holt and Co.| year=2008| isbn=978-0-8050-8037-7| url=https://archive.org/details/perfectscentyear00burr}}</ref>

====Fragrance bases====
[[File:Perfume Organ, Grasse.jpg|upright|thumb|A "perfume organ", where perfumers utilize hundreds of essences, in [[Grasse]], France]]
Instead of building a perfume from "ground up", many modern perfumes and colognes are made using ''fragrance bases'' or simply '''bases'''. Each base is essentially modular perfume that is blended from essential oils and aromatic chemicals, and formulated with a simple concept such as "[[Smell of freshly cut grass|fresh cut grass]]" or "juicy sour apple". Many of [[Guerlain]]'s ''Aqua Allegoria'' line, with their simple fragrance concepts, are good examples of what perfume fragrance bases are like.

The effort used in developing bases by fragrance companies or individual perfumers may equal that of a marketed perfume, since they are useful in that they are reusable. On top of its reusability, the benefit in using bases for construction are quite numerous:
#Ingredients with "difficult" or "overpowering" scents that are tailored into a blended base may be more easily incorporated into a work of perfume
#A base may be better scent approximations of a certain thing than the extract of the thing itself. For example, a base made to embody the scent for "fresh dewy rose" might be a better approximation for the scent concept of a rose after rain than plain [[rose oil]]. Flowers whose scents cannot be extracted, such as [[gardenia]] or [[hyacinth (plant)|hyacinth]], are composed as bases from data derived from [[headspace technology]].
#A perfumer can quickly rough out a concept from a brief by combining multiple bases, then present it for feedback. Smoothing out the "edges" of the perfume can be done after a positive response.