Dilution is more than turning down a volume knob
A material can seem sharp in one presentation and softer in another. A blend that felt full as a concentrate may seem different after the intended carrier is included. These observations do not necessarily mean that the material changed identity. Changing concentration can change what reaches the nose and how the impression is perceived.
The important distinction is between a liquid composition and an olfactory stimulus. “Ten times less concentrated in the liquid” describes arithmetic on a stated basis. It does not establish that the vapour above the sample, the perceived intensity or every facet of the scent will be ten times weaker.
Keep this as an interpretation problem, rather than a reason to use arbitrary evaluation dilutions. The examples below are records of already defined study presentations; they are not mixing levels or a skin-use recipe.
Intensity and character are separate observations
Gross-Isseroff and Lancet’s original study found that changing concentration could alter whether people judged the same odorant as qualitatively similar. Results differed between odorants and participants. The useful conclusion is conditional: concentration can affect perceived quality, rather than universally revealing one “true” smell.
A later original study by Keller and Vosshall recorded intensity, pleasantness and descriptive responses for many molecules at two concentrations. Its design keeps these responses separate. That is a useful discipline for a personal notebook too, without claiming that a home study reproduces the experiment.
Scroll sideways to see every column when needed.
| Question | Example observation | Avoid collapsing it into |
|---|---|---|
| Intensity | More or less noticeable in this presentation. | Quality, purity or suitability. |
| Character | A sharper edge or a creamier impression was noticed. | A different molecular identity. |
| Preference | This presentation was preferred for this study. | An objectively best concentration for every purpose. |
“Less intense but more clearly floral to me” is a coherent note. It does not contradict itself. The first part concerns the strength of the response; the second concerns the description the observer can give.
The liquid and the air are different parts of the system
A sample’s surrounding vapour is not a miniature copy of its liquid formula. Mata and colleagues’ perfume-modelling research considered liquid-phase interactions, solvent effects and the changing interface during evaporation. It supports treating release as a system-dependent question, not a direct percentage-to-smell conversion.
This matters when reading claims such as “alcohol opens the material” or “the carrier mutes it”. Those phrases might describe a person’s observation, but they leave the preparation, timing and comparison undefined. Ask what was actually changed before adopting an explanation.
Do not use logP alone to fill that gap. Octanol/water partitioning is not a measurement of the concentration reaching the nose from a particular carrier. The library’s logP and solvent-choice guide explains why those evidence types remain separate.
On a narrow screen, scroll the diagram sideways to read every label.
Make a concentration comparison interpretable
Start with a question such as “Does this established presentation make a particular facet easier for me to describe?” Identify the same supplied material in both records. Note the documented carrier, the strength and its basis, the presentation method and the observation context.
If the carrier changes at the same time as concentration, you are comparing preparations with more than one difference. That may be the actual question you want to ask, but call it a preparation comparison rather than isolating concentration. Similarly, a later observation of one sample and an earlier observation of another do not isolate concentration alone.
Preserve an unchanged reference and separate sample codes from expectations when practical. These steps improve the record; they do not make an informal exercise a calibrated sensory test. Use the existing one-variable comparison guide for the general study structure.
An example of careful wording
Two presentations, one identified source
These fictional notes refer to two documented evaluation preparations. A: “noticeable, sharp opening edge, hard to name”. B: “quieter overall, a soft floral association easier to describe”. No material-specific preparation values or measured results are implied.
The notes justify saying that the observer described the two presentations differently. They do not establish that B is purer, safer or more suitable for a commercial product. Nor do they show that everyone will make the same distinction.
A useful follow-up could compare the descriptions in a separate session under the same established method. If the difference is not repeatable, record that too. Rewriting the original note to match a desired story removes information that the later comparison could otherwise explain.
Keep evaluation strength separate from formula level
A concentration used to investigate a material is not automatically its appropriate formula level. A perfumer may need to understand an ingredient through a defined learning presentation and then consider its contribution in a completely different mixture. Those are separate decisions with separate evidence.
Remember the supplied preparation as well. If a bottle is already diluted, both the nominal named ingredient and its carrier enter the study record. Changing the bottle’s strength can change more than the number beside the ingredient name. Dilution maths supplies the arithmetic, while this article concerns the interpretation of what is perceived.
The useful habit is to record a relationship: “Under these conditions, this preparation made this aspect more apparent to this observer.” That is a stronger learning result than announcing one concentration as the definitive version of a material.
