One bottle of rose, one of patchouli, nine small numbered vials. Lesson four of the blending course builds a series from 9:1 to 1:9 to find the point where two scents stop standing apart and become one accord.
Two bottles, nine ratios
The two bottles in this lesson come from opposite ends of the evaporation chart. Damask rose is distilled from petals picked by hand at first light in Bulgaria and Turkey; the library records about 3,000 to 5,000 kg of fresh flowers for one kg of oil. Patchouli is distilled from leaves that have been dried and lightly fermented, each batch running 8 to 24 hours, with a yield of 2 to 4 percent of dry leaf weight.
On a blotter the two bottles keep different time. The library's volatility chart gives rose about 168 hours and places it in the heart. Patchouli is listed at 400 hours or more, in the base. One material stands in the body, the other in the ground. The pair is different enough to show clearly when they meet.
Lesson three ended with a gap: the ratio on paper and the ratio the nose hears do not coincide. Lesson four measures that gap systematically. Instead of guessing one ratio, all nine are set side by side and the blotters answer.
The nine ratios move in even steps: 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9. The first figure is rose, the second patchouli. The steps are even not because scent changes evenly, but because even steps make it possible to see where scent changes suddenly.
The series from 9:1 to 1:9
The series begins with dilution. Each oil is diluted to 10 percent in alcohol before the ratios are made, the practice perfumery calls a smelling dilution. Diluted, many materials open more clearly than they do neat. Rose is also one of the most expensive oils on the table; diluting first means the whole series of nine vials uses only a few drops of neat oil.
Each vial receives ten drops of diluted solution in total. Vial one: nine drops of rose, one of patchouli. Vial nine: one drop of rose, nine of patchouli. The whole series takes 45 drops of the rose solution and 45 of the patchouli solution. Shake gently, cap, number each vial.
Nine blotters are dipped at the same moment, each marked with its vial number and the time. The same moment is essential: if the dips are hours apart, differences on the blotters become differences of time rather than of ratio. The blotters are set apart and do not touch.
The smelling rhythm follows lesson two: five minutes, one hour, one day, three days. At each mark the blotters are smelled in order from vial one to nine, then back from nine to one. Smelling in both directions reduces the effect of a tired nose at the end of the row.
The point where two scents stop separating
At both ends of the series the answer is predictable. Vial one is rose with a shadow of earth behind it. Vial nine is patchouli with a trace of flower. The nose can still separate the two parts; the only difference is which one stands in front.
Moving towards the middle, there is one vial where the nose can no longer separate them. It is no longer rose plus patchouli but a third scent without a name. The library's glossary defines an accord at exactly this point: a few materials combined so that the nose reads them as one new smell rather than separate parts.
An accord is not an average. The 5:5 vial is not necessarily the most unified one. As lesson three showed, the two bottles differ in odour strength, so the point of balance tends to lean towards the weaker oil. Only the series shows where that point lies for the two lots actually on the table.
The point can also move over time. At five minutes the most unified vial may be 6:4. After a day, once the lighter part of the rose has thinned, it may shift to 7:3. A good accord holds together across several marks, not only the first.
Some pairs have no such point. Across all nine vials and four time marks, the nose can still separate the two parts. That is not a failure of the series but a result: the pair needs a third material as a bridge, or should not stand side by side in the same tier. Recording this in the notebook matters as much as recording a successful accord.
Geraniol meets patchoulol
Beneath the scent of the two bottles are two groups of molecules. In Bulgarian damask rose the library lists citronellol at 16 to 36 percent and geraniol at 16 to 26 percent. Geraniol is described as sweet rose with lemony, waxy facets, fresh and bright. It is a small terpene alcohol with a molecular weight of about 154.
On the patchouli side the main molecule is patchoulol, 17.5 to 32.7 percent of the oil, alongside α-bulnesene and α-guaiene. Patchoulol is a sesquiterpene alcohol with a molecular weight of about 222, smelling of warm wood and earth, slightly sweet, with a faint camphor trace, drier than patchouli oil itself.
The difference in molecular weight explains part of the difference in evaporation. Small molecules reach the nose first and leave the blotter sooner; large ones stay. In a rose and patchouli accord, geraniol and citronellol build the opening, patchoulol holds the end. The middle stretch is where both are present, and that is where the nose hears one scent.
Composition also explains why the same series gives different results from lot to lot. Turkish rose shows a wider range of geraniol, from 2 to 18 percent in the library's data. Indonesian patchouli usually carries more patchoulol than Chinese patchouli. Changing a lot changes the accord point.
Recording a series
A series is only worth something when it is recorded in the same format every time. The scent notebook from lesson one gains a table page: nine rows for nine vials, four columns for four time marks. Each cell holds three short items: which material stands in front, whether they can still be separated, and one or two words of description.
The descriptive words should stay within the vocabulary built in lesson one. If patchouli was written as damp earth in lesson one, lesson four uses damp earth too, not dark wood. A stable vocabulary makes it possible to compare series weeks apart.
Any cell where the nose can no longer separate the two parts is marked. After four time marks the marks form a zone on the table. A narrow zone means the accord is sensitive to ratio; a wide zone means the pair unites easily. Both are useful when the pair goes into a larger formula.
The nine vials should be kept, labelled, in a cool dark place. After one or two weeks, smell the same series again on fresh blotters. A rested blend often differs from a fresh one; the library's Blending 101 notes that the scent after 24 to 48 hours already differs from the first moment. Lesson seven returns to time as a material.
From a two material accord to three
A two material accord is the smallest unit of a formula. Once the most unified vial is found, it is handled as a new material: it has a name, a ratio, a description, and can be dipped on a blotter like any other bottle.
The next step is not a large third bottle but a very small amount. Lesson five takes this same rose and patchouli accord, adds in turn a drop of pink pepper, coriander seed and clary sage, and records how the direction of the scent changes. The series from lesson four becomes the control.
This series is for blotters. When the accord goes into a product worn on skin, damask rose has a maximum dermal level of 0.6 percent in the library's data, because it contains 0.5 to 3.3 percent methyleugenol. Patchouli has no IFRA concentration limit of its own, but since Regulation (EU) 2023/1545 it is on the list of fragrance allergens that must be labelled. Geraniol carries an IFRA limit of 5.3 percent in leave-on products.
The nine ratio method works for any pair: bergamot and cedarwood, lavender and geranium, any two bottles on the table. Each pair is a series, each series a page in the notebook.
Two bottles do not need to become one. They only need a ratio in which to do it.
That ratio is not in any book. It sits in one of the vials in the row.
Nine small vials, one single point.