The Perfumer's Art
Perfumery is an art as well as a science. The perfumer's art is based not on native ability, however, but on experience. A trained perfumer can recognize by odor a thousand different perfume ingredients and often tell their source and quality as well. He also has a vast amount of knowledge concerning the interaction of one odor with another, the staying power of different components, and the effect of various fixatives on the individual or mixed ingredients. In addition he may be aware of the chemical structure and possible chemical reactions of these substances. All this knowledge and experience are fundamental to compounding a perfume formula. In the final analysis, however, the sense of smell determines the character of the finished product.
Odor has thus far defined physical measurement and appropriate description. Only general terms such as spicy, sweet, heavy, fresh, woodsy, and floral are used, and these do not necessarily mean the same thing to different individuals. Several attempts have been made to classify odors, but no reliable system has been evolved. There is no correlation of odor with chemical structure or with botanical origin in perfume substances. Even the desirability of a particular scent seems to depend on the personality of the individual and on his previous odor associations.
Ingredients and Extraction Processes
Natural Ingredients. The natural products which go into perfumes are derived from both plant and animal sources. The chief plant materials used are essential oils, floral oils, and resins.
Essential Oils. Essential, or volatile, oils are complex mixtures of odorous substances found in a wide variety of plants and are produced chiefly by steam distillation. The oils may be present in one or more parts of a plant, such as the flowers, leaves, stems, barks, woods, roots, rhizomes, grasses, fruits or seeds. In the steam distillation process, the natural source material is suitably subdivided and placed in a large container with water. Heat is then applied by open fire, or by steam-heated coils or a jacket at the bottom of the container. The combination of water vapor and essential oil vapor thus driven off is led to a condenser, which generally consists of a coil arranged in a jacket or tank through which cold water flows. The condensed vapors are collected and allowed to separate, the oil floats to the top, and the water is drained off. In more modern installations the steam is produced separately and introduced into the container of raw material which is usually suspended in a basket or on a false bottom. Such apparatus can often handle as much as a ton of material at a time. The open-fire method is still employed on a small scale in remote areas.
The chief disadvantage of the steam distillation process is that the heat of the steam may bring about undesirable changes in the oil. Some of the most delicate and expensive flowers cannot be treated in this manner, but the rose and orange blossom are often steam distilled. Occasionally some component of the oil is soluble in the water, as in the case of the rose, which yields rose water as a by-product of steam distillation.
Some of the most commonly used essential oils are: lavender, vetiver, citronella, lemongrass, patchouly, rosewood, sassafras, peppermint, spearmint, sandal wood, cedarwood, clove, attar (or otto) of roses, cassia, and anise. Oil of lavender comes from the flowers and leaves of a plant grown mostly in southern France. The root of the vetiver is usually obtained from Reunion Island and Haiti and yields an oil of powerful and tenacious odor. Oil of citronella comes from Formosa, Guatemala, Java and Ceylon and is a well-known mosquito repellent. It contains gera-niol much used to impart a sweet note to perfumes. Lemongrass is an Indian plant whose oil contains citral, with a strong lemon odor, used as a base for other synthetics. Oil of patchouly is obtained from the dried leaves of a plant of Malaya and Sumatra. It has a warm, heavy odor.
The wood of a Brazilian tree is the source of oil of rosewood. This is the chief commercial source of linalool, an important isolate and perfume ingredient. Sassafras comes from the American root which is used in root beer and is a source of inexpensive soap perfume. Peppermint and spearmint are also American products employed chiefly in flavoring. Sandalwood oil is an East Indian product which has both fragrant and fixative properties. Cedarwood oil is another American product. Oil of cloves comes chiefly from Zanzibar and Madagascar and is used to give a spicy note to perfumes and as a source of eugenol in the synthesis of vanillin. Attar of roses has been a prized perfume ingredient for centuries and is now produced chiefly in Bulgaria. Cassia oil comes from the leaves and bark of a plant sometimes known as Chinese cinnamon. It is used as a flavoring ingredient and in soap-perfumes. Anise oil is distilled from the fruits of an evergreen tree of China and Indochina and is much used as a flavoring agent. Many other essential oils from all parts of the world are also used in perfumes.
The citrus oils, such as lime, lemon, orange, and bergamot, are also classified as essential oils but are produced by a method known as expression. In this method, mechanical pressure, or hand squeezing, is applied to the peels of the fruit, breaking up the oil cells and permitting the oil to run off. In the more primitive expression processes, the oil is simply soaked up with sponges and later squeezed out, collected, and strained. A more modern process employs hydraulic presses and centrifuges. Many of these oils contain large quantities of hydrocarbons known as ter-penes, which have a low odor value. These are relatively volatile and are frequently distilled off, leaving a more valuable terpeneless oil.
Floral Oils. These are similar in nature to essential oils but are obtained from the plant by a solubility or absorption process. They are produced mainly in southern France, Italy and North Africa (chiefly Morocco). Grasse, a small town in southern France, is the headquarters of the flower oil industry. There, thousands of acres are devoted to the cultivation of flowers for the production of perfume oils. The growers select the time of harvest with great care, attempting to provide blossoms which have oil of maximum quality and value. Different flowers are ready for harvest at different seasons of the year, so that almost continuous production is possible. The producers have generations of experience behind them and often possess trade secrets known only to their own families.
The flower oils are among the most expensive perfume ingredients. Some of the more important are those of the jasmine, tuberose, jonquil, rose, narcissus, hyacinth, violet, carnation, and orange blossom.
Three methods of production are employed. Extraction with volatile solvents is the most commonly used procedure. The flowers are placed in large containers known as extractors, together with a suitable solvent (usually highly purified petroleum ether). The extractor may rotate or the solvent may circulate as in a coffee percolator. The oil becomes dissolved in the solvent, and the resulting solution is led to a vacuum still. The solvent is distilled off and returned for re-use. The concentrated oil which remains is called a concrete and contains the perfume oils together with plant waxes. The concrete is in turn extracted with many times its own weight of pure alcohol in an apparatus known as a batteuse. Several batteuses together are called a battery. The perfume and some waxes dissolve in the alcohol, leaving behind other waxes which can be filtered off. The alcoholic solution is then frozen at 20° below zero to precipitate the soluble waxes, and the alcohol is removed by vacuum distillation, which leaves an expensive, easy-to-use, absolute flower oil. Yields may be as little as a pound of oil from a ton of fresh flowers and rarely are over one per cent. Jasmine absolute, considered inimitable and indispensable by the industry, is obtained in yields of approximately 0.15 per cent.
Another expensive and delicate method of production (formerly widely, but now rarely used) is known as enfleurage. After picking, the flowers are brought as rapidly as possible to nearby factories where no time is lost in placing the petals by hand on layers of fats made up primarily of highly refined lard. The fats, known as the corps, are laid out on both sides of a framed glass, known as the chassis. The chassis are stacked on top of one another so that the perfume cannot escape and be lost in the air. Absorption of the odorous oil by the fat takes place much as butter picks up food odors in a refrigerator. Actually more oil can be obtained by this method than was present in the flowers when harvested. This is possible because the flowers are still alive and continue to produce and exhale perfume. For this reason the flowers must be handled delicately and rapidly so that the life process is preserved and decomposition does not commence.
After a day the chassis is shaken so that the petals fall off, and those that do not come off easily are picked by hand. A new group of petals is then placed and the procedure repeated. The same corps is used over and over again for several weeks. When it is saturated with the perfume oil, it is heated up slightly, melted, and then resolidified into a uniform semisolid body called a pomade. In earlier days these pomades were used directly in perfumery, but they are difficult to handle and have a slight fatty odor. Now it is customary to extract the pomade with alcohol, producing a solution known as a pomade washing. The alcohol is then removed by vacuum distillation at a low temperature, leaving an oil known as absolute of enfleurage or absolute of pomade.
Enfleurage is used primarily for two flowers, jasmine and tuberose. In view of the delicacy of the process and of the value of the resulting product, many producers grow their own flowers and control every detail of each stage of production of flower and oil. The petals which have already been used for enfleurage are not thrown away, as they still contain some oils and waxes of definite perfume value. They are subjected to extraction with volatile solvents, and the oils obtained are called chassis.
Maceration is a process similar to enfleurage except that hot fats are employed instead of cold. The flowers are placed in cloth baskets suspended in the melted fat, which is heated in a water bath at 100° to 120°F. A continuous process is generally employed: the solvent flows over the flowers repeatedly, and the petals are replaced as soon as exhausted. The scent-laden fat is then treated with alcohol as in the enfleurage process. Maceration was employed extensively at one time but has now been largely replaced by extraction with volatile solvents. It is still useful for some flowers which wither quickly and give a poor yield by enfleurage. It is chiefly used at this time for the French rose, known as rose de mai, and for small amounts of orange blossom, hyacinth, and mimosa.
Resins. These are a group of sticky plant exudences variously called hard resins, soft resins, balsams, gums, and oleoresins. The subdivisions, however, are poorly defined and overlap one another. Resins are useful as blenders and fixatives. Since they are relatively easy to collect, they have been known since ancient times.
Benzoin is a hard resin which now comes chiefly from Thailand. It has a vanilla-like fragrance and contains vanillin. It is not present in healthy trees but is produced by wounding the
tree with incisions or by loosening the bark. Benzoin then oozes out and dries.
The useful balsams include balsam Peru, balsam tolu, balsam copaiba, and storax (or styrax): These are all viscous, colored liquids which are obtained directly from trees. The first two come from South America, where they ooze from the trees in liquid form and are collected with rags, which are then boiled in water, allowing the balsams to separate. Storax comes from trees in Asia Minor.
The most important gum is labdanum, which is a secretion of the leaves of the rockrose plant of Greece, southern France, and Spain. The leaves are either boiled in water or extracted with volatile solvents. Purification and further extraction yield an important fixative called ambrein. Other gums of lesser interest are opopanax, myrrh, and galbanum. All of these resinous substances are difficult to handle in the natural state and are usually extracted with benzene or alcohol, which is then evaporated, leaving a resinoid. The final preparation which the perfumer uses is a solution of the resinoid in a suitable solvent, often alcohol. The solution is called an infusion if prepared with heat, or a tincture if prepared in the cold.
Animal Products. The animal products used in perfumery are limited in number but of great importance, particularly as fixatives. The most widely used is castoreum or castor, which is obtained from the Canadian beaver as a by-product of the fur industry. The scent-bearing follicles are located near the genitals of both male and female beavers. Castor has an unpleasant odor which becomes more agreeable and somewhat spicy on dilution. It has a tendency to cause discoloration in perfumes.
Civet also has a powerful and revolting odor which becomes sweeter on extreme dilution. This substance is obtained from the scent pouches of both sexes of the civet cat, a native of Asia, the East Indies, and Africa. Commercial production has been developed only in Ethiopia. It is not necessary to kill the animal, which is kept in captivity and well fed. To obtain the valuable secretion, the animal is teased and aroused to a fury, and the scent bag is scraped. The civet, which is butterlike in consistency, is then packed in cattle and goat horns. It is an excellent fixative and also mellows or rounds out perfumes.
Musk is obtained from the male musk deer and is thought to be associated with sexual attraction in nature. The musk deer is small, no more than 20 inches high, and inhabits the Atlas and Himalaya Mountains. Chinese hunters kill the deer and remove the whole scent gland, drying it to a musk pod about the size and shape of a walnut. It is actually unnecessary to kill the animal, and development of production from captive animals would prevent the slaughter which threatens extinction of the species. The finest musk—musk tonquin—comes from Tibet.
Ambergris is well known and highly appreciated by the perfumer. This substance is developed by the whale, and it is believed that only the male of the species produces it. Apparently it is a calculus formed in the intestinal tract when irritated by the indigestible beaks of the squid. It is found on beaches or floating in the sea, or in the dead animal in various-sized lumps ranging up to 300 pounds. Ambergris is extremely valuable for the creation of high-grade perfumes.
Synthetic Ingredients. Synthetics and isolates, or aromatic chemicals, are substances of known chemical structure isolated or derived from natural products or built up in the laboratory from simple chemical substances. In the past 100 years nearly all natural perfume ingredients have been subjected to analysis, and attempts have been made to duplicate the isolated chemicals synthetically. In addition, many entirely new chemicals have been discovered which are of value to the perfumer. These chemicals have not replaced the natural substances on the perfumer's shelf, but they have provided valuable and now indispensable supplements. Literally thousands of chemicals are now available to the perfumer, and many low-priced industrial perfumes today consist largely of synthetic aromatics.
Aromatic chemicals may be classified in several ways. Some are isolated or derived from essential oils; others" are completely synthetic. Some are found in nature, and others are unknown in nature. Finally, some closely resemble flowers or other perfumes in odor, while others possess an independent character with little or no resemblance to nature's odors.
Some important perfumery isolates are geran-iol from palmarosa, or citronella oils, citronellal from citronella oil, rhodinol from geranium oil, linalool from rosewood oil, terpineol from pine oil, citral from lemongrass oil, eugenol from clove oil, safrole from sassafras and camphor oils, and cedrol from cedar oils. Some substances secondarily derived from essential oils are hydroxy-citrononellal from citronellal, isoborneol and terpineol from pinene found in turpentine oil, heliotropin from safrole, and the ionones and methyl ionones from citral. In contradistinction to these naturally derived substances are many aromatic chemicals built up wholly synthetically, such as the synthetic musks, called musk xylene, musk ambrette, and musk ketone : phenylethyl alcohol which has a rose odor; methyl salicylate or artificial oil of wintergreen; coumarin with a sweet, woody and hay-like odor; benzyl acetate with a jasmine-like odor; pheny-lacetaldehyde with a powerful hyacinth odor; cinnamaldehyde with a cinnamon odor and flavor; and cyclamen aldehyde with a cyclamen odor. Vanillin bridges these categories, as it may be made from eugenol found in clove oil or synthesized from synthetic guiacol.
Many of the chemicals already mentioned, including all isolates, may be found in nature. In addition, vanillin is found in the vanilla plant, in oil of cloves, in several resins, and in a number of other diverse sources. Coumarin occurs in the tonka bean, in oil of lavender, in oil of cassia, in several species of orchids, and in a number of other natural sources. Phenylethyl alcohol is found in oil of rose and several other flower oils. Benzaldehyde was first noted in bitter almond oil. On the other hand, some aromatics such as a cyclamen aldehyde, hydroxycitronellal and phenylacetaldehyde are completely unknown in nature. The ionones were synthesized in the laboratory years before any natural source was detected.
Certain of these aromatic chemicals resemble nature's odors very closely. The ionones all possess violet odors, and phenylethyl alcohol has a definite rose odor. Cyclamen aldehyde faithfully reproduces the odor of cyclamen flowers. On the other hand, the odors of other chemicals are actually unknown in nature and are difficult to describe. Hydroxycitronellal exhibits a lily
of the valley odor. Terpineol has a woody-lilac odor.
Aromatic Specialties. In addition to the many natural and synthetic products already mentioned, there are a number of prepared blends called aromatic specialties, which are sold by the larger essential oil houses. Many of these products are formulated from aromatic chemicals and essential oils not usually offered to the trade. The large concerns have extensive experience in making up a given odor for a particular price range or purpose. The specialties are then used as bases by other perfume manufacturers.
Manufacture and Marketing
Preparation. The perfume that is sold on the market today consists of a blend of several perfume ingredients, diluted in alcohol to a certain concentration. As few as 10 ingredients may be used or as many as 200. The perfumer usually starts with a base that will contribute the main note he is seeking to create. This base may be one or several essential oils, or aromatic chemicals, or an aromatic specialty already compounded to give a particular effect. To this background note are added smaller quantities of other substances to round out, blend, harmonize, or bouquet a perfume. Finally, small amounts of appropriate fixatives must be added to render the odor more permanent.
These ingredients are all weighed very carefully, mixed, and heated gently to insure homogeneity. Pure 95 per cent alcohol is then added, followed by a small amount of water, and the mixture is brought up to volume with specially denatured alcohol. The perfume is chilled for several days to hasten precipitation of insoluble substances and then filtered. Aging is the next step in the process. Some perfumes are bottled immediately and aged in the bottle, while others are aged in bulk form for two months, refiltered, and then bottled. Aging for a year is desirable before sale, to allow time for interactions which might change the final odor.
Fixatives. These are important components of any finished perfume. They bind the ingredients together, diminishing the rate of evaporation of the more volatile components and rendering the odor more permanent. If no fixatives were available, the odor of a compounded perfume would change with time as the more volatile components evaporated, leaving a residual of less volatile chemicals with a different scent. An ideal fixative would cause all the different components to evaporate in constant proportion. No substance known does this to perfection, but many have marked fixative properties. Alcoholic tinctures of the animal substances such as civet, ambergris, and musk are very effective in this respect. The synthetic musks are genuine fixatives, as are the odorous resins and balsams. Certain resinoids prepared from such sources as patchouli leaves, cloves, nutmegs, and peppercorns impart their own characteristic odor and also act as fixatives. Some of the synthetic chemicals and isolates function in the same manner—for example, vanillin, coumarin, eugenol, benzyl cinnamate, benzyl benzoate, and linalyl benzoate. A few odorless chemicals are also known to have fixative powers, such as the esters of adipic acid and glycerol monooctadecyl.
Concentration. The final concentration of perfume substance in alcohol varies from eight ounces to three pounds in a gallon (128 ounces) of the finished product. The average is about 24 ounces to the gallon. The final concentration varies not so much with the value of the product as with the type of perfume. Heavier odors, Oriental types, and strong floral notes like gardenia cannot be made up in the same strength as light and evanescent odors. Toilet waters and colognes are more dilute, ranging from two to eight ounces per gallon. In the United States, the terms toilet water, cologne, and eau de cologne are almost always used synonymously. A few manufacturers retain the European practice of limiting the terms eau de cologne and cologne to preparations with a citrus oil base.
Industrial Uses. Perfume is used in all types of cosmetics and soaps, and to mask, modify, or improve the odors of such diverse articles as raincoats, stockings, inks, pastes, paints, insecticides, and toys. Specific smells have been duplicated and applied in appropriate circumstances. Among the odors duplicated are those of fresh bread, burned wood, varnish, the interior of a new car, wet earth, fresh cake, pine trees, and leather. Such industrial uses are increasing rapidly.