Three Concepts, Three Separate Questions
When evaluating a fragrance it is easy to conflate three things. Yet sillage, projection and longevity each answer a different question. Let us define the concepts precisely first; everything else comes down to measurement.
Sillage is the scent trail you leave behind after you pass through a space — the line you draw in the air. Projection is how far the scent radiates from the skin — the diameter of your personal scent bubble. Longevity is time: how long the fragrance remains perceptible.
A fragrance can project powerfully while leaving little trail. Another may sink into your skin and linger there for hours without travelling even a step further. Measuring all three separately is the first step towards interpreting a formula correctly.
Seeing the Differences at a Glance
Placing the three concepts side by side clarifies which question each one asks. The table below is the framework a formulator should keep in mind when reading a formula.
| Concept | Question | Determined by | How it is perceived |
|---|---|---|---|
| Sillage | What trail do I leave? | The strength of diffusing molecules and the trail left by movement | Others, after you have passed by |
| Projection | How far does it reach? | High-volatility, powerful raw materials | A person standing at a certain distance |
| Longevity | How long does it last? | The volatility of the raw materials (not the ratio) | You and those close to you over several hours |
Note: there is no "ratio" column in the table. That is because performance is not determined by the fragrance oil percentage alone. We explain this in the next section.
Longevity Is Not Concentration
The most common mistake: "If I increase the ratio, it will last longer." This is wrong. What truly determines longevity and sillage is the volatility of the raw materials in the formula — that is, how quickly a substance disperses into the air.
Push a citrus-heavy blend to 25 % and it will still evaporate quickly, because top note molecules are light and fast. By contrast, a 10 % formula built on heavy base note materials such as amber, oud and musk can speak from the skin for hours. It is about structure, not percentage.
For the same reason, do not treat labels such as EDP or EDT as absolute performance guarantees. These are approximate concentration bands; the volatility balance of the formula determines final performance. When building your note architecture, use the Top–Middle–Base Note Pyramid as your foundation.
Two different structures at the same ratio behave very differently:
| Formula | Fragrance oil ratio | Structure | Expected behaviour |
|---|---|---|---|
| A | ~20 % | Citrus + volatile green notes | High initial projection, short longevity |
| B | ~10 % | Amber + musk + resins | Low opening, long and close-to-skin longevity |
| C | ~15 % | Balanced pyramid + fixative | Moderate projection, balanced trail and duration |
How to Measure in Practice
"Feeling" performance is not enough — you need consistent measurement. When you repeat the same method every time, you can make honest comparisons between formulas. Here is a straightforward evaluation protocol.
- Start with a paper strip
Apply an equal amount to a blotter strip (blotter). Track the top notes in the first few minutes and the dry-down over several hours. The strip reads the raw structure independently of skin.
- Test on skin
The behaviour observed on a strip will change on skin. Apply a standard amount (for example 1–2 sprays) to the inner wrist and do not rub. Skin temperature and pH both affect performance.
- Measure projection by distance
At set intervals (for example after the first hour, then every few hours) note whether you can detect the scent from an arm's length away. Keep the distance consistent.
- Test sillage with movement
When you move your arm through the air, does a trail remain? Ask someone else whether they detect a scent after you have passed. Sillage is best measured with a second person.
- Log longevity hourly
Record the perception level on a scale (e.g. 5 = strong, 1 = skin-close trace). Follow the curve of "how it fades" rather than just "when it disappears".
Do not treat the time intervals as absolute targets. They vary from person to person, with ambient humidity and with the season. What matters is that you compare your own formulas under the same conditions. Consistency is more valuable than any absolute figure.
Improving Performance and Frequently Asked Questions
You have measured and identified the shortcomings. Now it is time to refine the formula. Two adjustments come into play here: maceration and structural reworking.
Maceration is more than simply waiting. Alcohol interacts with the fragrance oil; mild esterification reactions allow the scent to settle and reduce the harsh "alcohol spike". Maceration at room temperature (~15–20 °C), protection from light and, finally, cold filtration (removing waxy particles to achieve clarity) improve both scent and appearance.
Pay attention to solubility as well: adding too much water to high-strength ethanol will cloud the blend and cause phase separation. Keep the water ratio low, start with a small amount, test clarity at every step, and use a ready-made perfumer's alcohol or a suitable solvent where needed. For the fundamental workflow, follow the sequence set out in the Beginner's Guide to Making Fragrance from Scratch.
Performance also depends on raw materials. Understanding the differences between a fragrance oil, a parfum oil and an essential oil allows you to anticipate how each material will behave — explore that topic separately.
If sillage is low, should I increase the fragrance oil ratio?
Is an EDP always longer-lasting than an EDT?
Is a high ratio always safe?
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