It isn't your nose: dilution is the first real skill

Last time we picked ten materials. This time, the one technical skill worth learning before you blend anything: dilution.

The most common early frustration is "I can't tell the difference". You open three bottles, they're all sharp and loud, and by the fourth your nose has given up. The conclusion is usually: maybe I'm not cut out for this.

Hold off on the talent verdict. The problem is concentration: you're smelling everything at full strength.

Neat is not how a material appears in a formula

Materials are almost never used neat. A typical fragrance sits at 15–25% concentrate, and a single material inside that might be 0.5%. What you smell at the bottle neck and what that material actually contributes to the finished thing are two different objects.

The indole in jasmin from last time is the standard example, faecal neat and floral once diluted, and the same shift repeats across the palette:

• Musks are nearly odourless neat, yet at 1% they visibly change how long everything lasts and how round it sits
• Aldehydes choke you neat. The first time I smelled them straight from the bottle I coughed for a good minute. At 0.1% you finally get that bright, soapy shimmer
• Patchouli goes from mould and soil to a clean woody floor once diluted

Smelling neat, you meet each material at its least characteristic.

A hundredfold difference in concentration is a different smell

That heading is meant literally. In 1988 Gross-Isseroff and Lancet measured it directly in Chemical Senses: subjects compared pairs of samples and judged only whether they were qualitatively "similar" or "different", and the pool included the same odorant at different dilutions.

While pairs with the same odorant at identical concentrations were judged "similar" in >90% of the cases by all subjects, scores went down to ≤10% "similar" judgements in some cases when the same odorant was presented at a 100-fold concentration difference.

Dilute the same bottle a hundredfold and perception treats it as a different odour. The authors note this parallels effects already documented in vision and hearing.

That explains the two most common beginner complaints:

• "I know this material — why can't I find it in the formula?" You smelled it neat; in the formula it sits at 0.5%.
• "Everyone calls this floral and it smells faecal to me." Same molecule, different concentration.

So the concentration you smell at is not an operational detail. It decides which odour you are smelling.

What strength

There's no single answer, but there is a practical starting set:

Strength	Use
10%	Default for daily evaluation. Most materials sit closest to their formula role here
1%	Loud materials: indoles, aldehydes, some spices, animalics
0.1%	Extreme ones: certain sulphur compounds and pyrazines, where one drop ruins a batch
30%	Weak, slow materials: some resins and woods

In practice, make everything at 10% and add a 1% for the loud ones. You don't need all four steps up front; that comes later, when you're studying one material closely.

Kit: less than you think

All you need:

• A scale reading to 0.01g. The one thing you can't skip
• Small glass vials, 10ml, as many as you can get
• Blotters, proper ones; copy paper has a smell of its own
• Disposable pipettes
• Labels

You don't need a measuring cylinder. Weigh everything instead of measuring volume: densities vary enough that volume measurements make your notes unreproducible.

A repeatable routine

For a 10% solution, 10g total:

1g   material
9g   ethanol

Tare the empty vial, add material to 1.00g, top up with ethanol to 10.00g. Shake it, label it: material, strength, date.

The date matters. Citrus oxidises; some materials mature. Three months from now you'll want to know how old the vial in your hand is.

How to smell

There's technique here too.

Touch the blotter to the liquid rather than soaking it. Too much and the first few minutes are just solvent.

Write it down, and be specific: what it resembles, what it reminds you of, whether it's dry, sweet, metallic. "Nice" tells you nothing a week later. Your vocabulary will be poor at first; mine was. It grows on the page, through the act of writing.

Stop when you're tired. Five or six materials in a row is the limit, and past that everything smells the same; you're wasting material while building false memories. Some people reset on their own forearm or coffee beans, with varying results. Rest always works.

Smell the same thing at different times: on contact, ten minutes, an hour, the next day. A material's full shape is a curve over time.

A common misreading

"Dilution is to save money" gets it backwards. The point is to smell what the material actually is; the savings come along for free.

If you only do one thing: make a 10% of each of last article's ten materials, smell them for a week, write it down. By the end of that week you'll understand those ten better than most people who only read.

References

R. Gross-Isseroff & D. Lancet, Concentration-dependent changes of perceived odor quality, Chemical Senses, 13(2), 191–204 (1988). doi:10.1093/chemse/13.2.191