Bài 2 · Một que thử, ba ngày

Seven strips of white absorbent paper, each as long as a hand, labelled at the top with the oil and the dipping time. Five minutes later, all seven smell. Three days later, only a few still smell clearly. The second lesson of the blending course turns time into a tool: one blotter, a series of checkpoints, and a self made evaporation chart.

The paper blotter

Absorbent paper holds an essential oil across a wide surface and lets it evaporate freely. That is why the blotter, or mouillette, is the perfumer's standard tool: a strip of paper used to smell materials and to follow how a scent changes over time. On skin, a scent is also affected by body heat, moisture and the skin's own oils. On paper those variables almost disappear, and what remains is the behaviour of the material itself.

That behaviour has a name. The vapour pressure of a substance shows how readily it evaporates: molecules with high vapour pressure reach the nose first and fade early, those with low vapour pressure linger. The time a material stays perceptible on a blotter or on skin is called tenacity, usually recorded in hours or days on a blotter.

The familiar division into top, heart and base has a clear origin. In 1955, W. A. Poucher published a classification of odours by evaporation coefficient in the journal of the Society of Cosmetic Chemists, and perfumers have used it as a basis for sorting notes into tiers. This lesson repeats that measurement at the scale of a table: no laboratory, only paper, a pen and a clock.

Dip, label, time

The process begins before the bottle is opened. Each blotter is labelled in pencil with the oil and the dipping time, at the top end that stays dry. One oil per blotter, and only one blotter. Each is dipped to the same depth, about one centimetre, then lifted out and held still for a few seconds so the excess drips back into the bottle.

The blotters need to stand apart, not touching, in a clip stand or pushed into a block of foam, in a ventilated corner without direct draught, away from heat and sunlight. If two blotters touch, oil from one soaks into the other, and every note afterwards is wrong. Seven blotters is a sensible number for a first run: enough to see the tiers, not too many to follow.

One choice must be written down: neat or diluted. The data source the library uses measured materials neat, except for a few cases such as vanilla, measured at 20 percent. To compare with the library chart, this lesson dips neat. For very dense oils, an extra blotter at 10 percent in ethanol can be added, clearly marked.

Seven oils for a first run can come from the set of ten in the previous lesson: bergamot, peppermint, lavender, geranium, ylang ylang, frankincense and patchouli. Cedarwood can replace one of them. The dipping order does not matter, as long as each dipping time is recorded to the minute.

Five minutes, one hour, one day

Each checkpoint shows a different part of the same oil. At five minutes, the lightest fraction is leaving the paper, and the smell is often sharp, bright, sometimes harsh. At one hour, the light part has clearly dropped; many oils show their real face here. At one day, only the heavy molecules remain. At three days, the nose is smelling the base, the stage perfumery calls the dry down.

Top note, heart note and base note are three names for one phenomenon: differences in volatility. The glossary defines the top note as what is perceived in the first minutes, carried by fast evaporating molecules such as monoterpenes and light esters, and the base note as the slowest part, remaining for hours to days, usually woods, resins, mosses, musks and vanilla. The blotter lets those definitions be checked by nose, one checkpoint at a time.

A notebook page for this lesson takes the form of a table. The rows are the seven oils. The columns are five checkpoints: five minutes, one hour, four hours, one day, three days. Each cell records two things: an intensity score from 0 to 5, and a few descriptive words. The score need not be precise. It only needs to be consistent across one person's cells.

Each time, the blotter is brought to the nose at the same distance, smelled briefly, then returned to the stand. Short pauses between blotters help avoid olfactory fatigue. A cell scored 0 means the blotter no longer smells to that person; the first checkpoint scored 0 is the most important figure in that row.

Bergamot leaves, patchouli stays

The two ends of the table are usually the clearest. Bergamot is a pressed peel oil, mostly limonene and linalyl acetate, two light molecules. It is brilliant at five minutes and fades quickly afterwards. The library's data source has no hours of its own for ordinary pressed bergamot; the only figure is 8 hours, measured on bergapten reduced bergamot. The library chart therefore places bergamot in the top tier as an estimate.

At the other end is patchouli, distilled from the dried leaves of Pogostemon cablin. Its main constituent is patchouli alcohol, with alpha bulnesene and alpha guaiene, all sesquiterpenes, large and heavy. The source records patchouli as recognisable on a blotter for 400 hours or more, over two weeks, and 400 hours is that source's ceiling. At three days, the patchouli blotter still smells clearly, while the bergamot blotter beside it went quiet long before.

Cedarwood gives a lesson in names. The Cedarwood oil in the library chart is Himalayan cedar, Cedrus deodara, recorded at 400 hours or more. Virginian cedarwood, however, is Juniperus virginiana, a juniper, with alpha cedrene, thujopsene and cedrol. Both are called cedarwood and both sit in the base, but on two blotters side by side they are two different woods.

Between the two ends is the most interesting part. Peppermint is recorded at about 16 hours. Geranium about 28 hours. Ylang ylang about 140 hours. Frankincense about 188 hours, opening on a fresh terpene note and drawing out a long resinous tail. Those figures show that the borders between tiers are not walls but a continuous band.

Comparing with the library chart

The library's volatility chart places the 57 oils Lê Mai sells into three classes, and records blotter hours from The Good Scents Company's substantivity figures. The hours fall into five bands: under 12 hours very fast, 12 to 48 hours fast, 48 to 150 hours medium, 150 to 300 hours long, 300 hours and above very long.

Comparing a self made chart with that one reveals a few deliberate mismatches. Lavender is recorded at 8 hours but placed in the heart, because the class reflects role in a blend and main constituents, not hours alone. Lemongrass is recorded at 92 hours but placed on the border of top and heart. Ylang ylang and frankincense are placed from heart into base. The top, heart and base division is a simplified model; in practice the tiers overlap.

The library chart also states its own limits. Blotter hours are not wear time on skin, in soap or in candles. Temperature, dilution, the lot and the sensitivity of the nose all shift the figure. The chart is for relative comparison, not precise prediction. The same holds for a self made chart.

A chart of one's own

After three days, the notebook table has seven rows and five columns, and each row has a point where the smell ends. Sorting the seven rows by that point, earliest to latest, gives a volatility chart belonging to the person who smelled. The order is usually close to the library chart but rarely identical, because each nose has its own thresholds.

The mismatches are data, not errors. A blotter that fades earlier than the library chart may be down to the nose, a room that was too warm, or a different lot of oil. Recording the room temperature and the lot number of each bottle lets the next run be compared with this one.

The third lesson uses this chart for a first piece of work with proportions: choose one top, one heart and one base oil, and see how the three tiers share a single blotter. That lesson is Lesson 3 · Three Tiers of a Scent. The set of ten bottles and the notebook method are introduced in Lesson 1 · Ten Bottles and a Notebook.

A printed chart gives the order.

A blotter shows the order taking place.

Three days, one strip of paper, and the tiers appear by themselves.