Cologne · vỏ cam, hoa cam và hương thảo

Three peels, one flower, a sprig of herb and a bottle of alcohol. Eau de Cologne has crossed more than three centuries with little else, and it leaves the skin faster than almost any other form of perfume.

A Scented Water from the Eighteenth Century

On 13 July 1709 Giovanni Battista Farina founded a company in Köln, the city the French call Cologne. Johann Maria Farina, of the same family, composed a scented water from citrus oils and named it after the city. According to the German Patent and Trade Mark Office, Johann Maria Farina gegenüber dem Jülichs Platz is the oldest perfume manufacturer still in operation. The Farina house in Köln is now a fragrance museum.

The original formula was not complicated. Citrus peel oils made up most of it, orange flower and orange leaf joined in, lavender or rosemary added an herbal line. Everything was diluted in alcohol at a low strength. No heavy resins, no animal musks, no thick base. The scent rose quickly and fell just as quickly.

Later the name came loose from its maker. Eau de Cologne became the name of a style and, at the same time, the name of the most dilute form of perfume. In 1853 Pierre François Pascal Guerlain made Eau de Cologne Impériale for Empress Eugénie. In 1966 Edmond Roudnitska made Eau Sauvage for Dior, placing lemon, bergamot, basil and rosemary beside Hedione, a transparent jasmine-like molecule.

More than two hundred years separate those three bottles, yet the frame barely moved: citrus peel on top, flowers in the middle, herbs running through, a thin base. Few structures in perfumery have lasted as well.

Bergamot, Lemon, Orange Blossom

A citrus peel holds small oil sacs just under the surface. Cold pressing breaks those sacs without heat, and the oil comes out together with heavy non-volatile compounds. This is how the bergamot and lemon in a cologne are obtained.

Bergamot is grown almost entirely on a narrow coastal strip in the province of Reggio Calabria, at the southern tip of Italy; about 90 percent of world production comes from there. In the oil, limonene makes up about 28 to 45 percent, linalyl acetate 18 to 28 percent, linalool 4 to 20 percent. Linalyl acetate is the ester that gives bergamot its sweet, lightly floral, cool smell. Because of it, bergamot is softer than other peels and bridges into the floral layer.

Cold pressed lemon is sharper. Limonene accounts for about 56 to 76 percent, with β pinene, γ terpinene and a small amount of citral, whose two isomers geranial and neral give the bright, sharp lemon edge. Each tonne of peel yields about 5 to 8 kg of oil. Sicily and Calabria in Italy are the reference regions, alongside Argentina, Spain and the United States.

Orange blossom follows another route. The bitter orange tree gives three oils from three parts: neroli steam distilled from the flowers, petitgrain distilled from leaves and young twigs, and a peel oil cold pressed from the fruit. Neroli holds roughly 31 to 54 percent linalool and smells floral, fresh, lightly sweet, with a green streak. Being distilled from flowers, neroli contains none of the furocoumarins found in peel oils.

Those three materials are three speeds. Lemon peel leaves first. Bergamot stays a little longer thanks to its ester. Orange blossom holds the middle once both peels have thinned.

Rosemary and the Herbal Line

A sprig of rosemary rubbed between two fingers smells clean, slightly camphoraceous, close to eucalyptus. Most of that smell comes from 1,8-cineole. But rosemary oil is not one uniform material: the plant has several chemotypes, and each gives different proportions.

In the cineole chemotype, 1,8-cineole makes up about 39 to 58 percent. In the camphor chemotype, camphor rises to about 17 to 27 percent and the smell turns heavier and warmer. The verbenone chemotype is softer but carries a lower use limit. For a cologne that needs clarity, the cineole chemotype is the neatest choice; note that it should not be used near the faces of children under six.

In the classification of the French Society of Perfumers, the aromatic citrus branch is where the herbal part grows until it is half the scent rather than a detail. Classic Eau de Cologne already had rosemary and lavender beside the citrus; this branch simply brings that part forward.

Lemon leaf is another connecting thread. The oil distilled from the leaves holds about 25 to 35 percent geranial and 18 to 26 percent neral, far richer in citral than the peel. The smell is green and tart, closer to leaf than fruit. Citral is also why lemon leaf has a low skin limit, 0.6 percent, because of the sensitisation risk.

Low Strength, Short Life

Limonene is a monoterpene, a small, light, fast-evaporating molecule. In a cologne, most of the oil by weight is molecules like it. They belong to the top note, the part of a scent noticed in the first minutes.

Strength does the rest. Eau de Cologne as a concentration usually holds only about 2 to 5 percent concentrate in alcohol; eau de toilette about 5 to 15 percent. Little concentrate, made mostly of light molecules, means the scent spreads widely at first and then thins noticeably. The post Same Scent, Four Strengths goes further into these grades.

Modern citrus perfumes solve the brevity with synthetic molecules: synthetic musks and Hedione keep a fresh impression on skin for several hours, noticeably longer than a classic cologne. The classic cologne does not solve it. It accepts it.

That is a design, not a flaw. A light, bright scent that then disappears is exactly what the formula sets out to do. The fragrance pyramid of top, heart and base is a simplification; in a cologne the top is almost the whole story, and the base is only enough to keep the tail from breaking off abruptly.

The Lê Mai Cologne Blend

A homemade cologne starts with measurement, not inspiration. The blend below uses six oils that each have a page in the Lê Mai library, diluted at 5 percent in perfumer's alcohol, the upper end of the eau de Cologne range. A 30 ml bottle, 30 drops of essential oil in total.

The structure reads from the top down. Bergamot FCF is the main body, a third of the blend. Cold pressed lemon gives the sharp edge. Neroli holds the middle. Cineole rosemary draws a clean herbal line. Two drops of lemon leaf add a green streak of citral. Atlas cedarwood forms a thin, dry base, just enough to keep the tail from dropping straight away.

On a blotter the blend passes through three stages. The first minutes are lemon peel and bergamot, bright, slightly sour, with the green streak of citral from the leaf. Then orange blossom shows, softer, and rosemary rises beside it like a fine drawn line. At the end what remains is dry cedar and a little of neroli's linalool, very light, almost only a trace. None of the stages lasts long; that belongs to the structure, not to this blend alone.

Once the drops are in the alcohol, the bottle should be sealed and left to rest before use; the term for this stage is maceration, usually a few days to a few weeks, while the scent settles and knits together.

Checked on the 5 percent finished product: cold pressed lemon at 20 percent of the blend becomes 1.0 percent on skin, half of the IFRA phototoxicity limit of 2.0 percent. It is the only phototoxic oil; bergamot FCF sits at 1.7 percent, far below its 16.6 percent ceiling.

The oil closest to its limit in proportion is lemon leaf: about 0.33 percent on skin against a 0.6 percent maximum set by its citral. Do not raise it above two drops in a 30 ml bottle. Neroli, cineole rosemary and Atlas cedarwood carry no specific skin limit in the library data at these levels; cineole rosemary should not be used near the faces of children under six.

Swapping bergamot FCF for ordinary cold pressed bergamot would bring in the 0.4 percent limit and the additive rule with lemon, pushing the blend over. Do not swap.

Pressed Lemon and the Phototoxicity Limit

Furocoumarins are heavy, non-volatile molecules. They do not travel with steam during distillation, but they come out with the oil when peel is cold pressed. That is why distilled lemon is not phototoxic while cold pressed lemon is, mainly because of bergapten and oxypeucedanin.

The library's phototoxicity page lists IFRA maximum skin levels for each peel oil: cold pressed bergamot 0.4 percent, cold pressed lime 0.7 percent, cold pressed lemon 2.0 percent. These limits apply to leave-on products; rinse-off products are generally exempt. Above them, skin should avoid UV light for 12 to 18 hours after application.

That is why the blend uses bergamot FCF. It has had its bergapten removed by fractional distillation; under the EU scientific committee's bergapten threshold, bergamot FCF can be used up to 16.6 percent on skin. Lemon stays cold pressed, because its sharp edge is hard to replace, but it is counted carefully. When several phototoxic oils are used together, the risk adds up in proportion; here there is only one.

Furocoumarin content in pressed lemon can vary up to twentyfold between sources. The IFRA limit accounts for that, but it does not make the limit optional. The post Lemon Peel and Sunlight goes deeper into how the reaction works.

A cologne does not try to stay.

It is built to pass through, and to pass through well.

Three centuries on, the formula still needs only peel, flower and a sprig of leaves.